Non-aqueous secondary battery and its control method

ABSTRACT

The invention provides a non-aqueous secondary battery having positive and negative electrodes and non-aqueous electrolyte containing lithium salt which has an energy capacity of 30 Wh or more, a volume energy density of 180 Wh/l or higher, which battery has a flat shape and is superior in heat radiation characteristic, used safely and particularly preferably used for a energy storage system. The invention also provides a control method of the secondary battery.

FIELD OF THE INVENTION

[0001] The present invention relates to a non-aqueous secondary batteryand its control method, particularly to a non-aqueous secondary batterypreferably used for a energy storage system and its control method.

DESCRIPTION OF THE PRIOR ART

[0002] A household distributed power-storage system for storingnighttime power and photovoltaic power and a energy storage system foran electric vehicle have been recently noticed from the viewpoints ofeffective use of energy for resource saving and global atmosphericproblems. For example, Japanese Unexamined Patent Publication No.6-86463 discloses a total system constituted by combining a power supplyfrom a power station, gas co-generation system, a fuel cell, and astorage battery as a system capable of supplying energy to energyconsumers under an optimum condition. A secondary battery used for theabove energy storage system must be a large scale battery having a largecapacity unlike a small secondary battery for a portable devise havingan energy capacity of 10 Wh or smaller. Therefore, the above energystorage system is normally used as a battery system constituted bystacking a plurality of secondary batteries in series and having avoltage of 50 to 400 V and in most cases, the system uses a lead-acidbattery.

[0003] In the field of a small secondary battery for a portable devise,a nickel-hydrogen battery and a lithium secondary battery are developedas new batteries in order to correspond to the needs for a small sizeand a large capacity and therefore, a battery having a volume energydensity of 180 Wh/l or more is marketed. Particularly, because a lithiumion battery has a possibility of a volume energy density exceeding 350Wh/l and is superior to a lithium secondary battery using metal lithiumas a negative electrode in reliabilities such as safety and cyclecharacteristic, the market of the battery has been remarkably expanded.

[0004] Therefore, also in the field of a large scale battery for aenergy storage system, development is energetically progressed byLithium Battery Energy Storage Technology Research Association (LIBES)or the like by targeting a lithium ion battery as a prospective productof a high energy density battery.

[0005] The energy capacity of the large lithium ion batteryapproximately ranges between 100 Wh and 400 Wh and the volume energydensity of the battery ranges between 200 and 300 Wh/l, which reachesthe level of a small secondary battery for a portable devise. Typicalshapes of the battery include a cylindrical shape having a diameter of50 to 70 mm and a length of 250 to 450 mm and a prismatic shape such asan angular box shape or a boxed shape with rounded edges having athickness of 35 to 50 mm.

[0006] Moreover, as a thin lithium secondary battery, the following aredisclosed: a film battery using a film obtained by laminating a metaland a plastic for a thin case and having a thickness of 1 mm or less(Japanese Unexamined Patent Publication Nos. 1993-159757 and 1995-57788)and a small prismatic battery having a thickness of 2 to 15 mm (JapaneseUnexamined Patent Publication Nos. 1996-195204, 1996-138727, and1997-213286). Purposes of these lithium secondary batteries correspondto decrease of a portable devise in size and thickness. For example, athin battery which has a thickness of several millimeters and an area ofapprox. JIS size A4 and which can be stored on the bottom of a portablepersonal computer is also disclosed (Japanese Unexamined PatentPublication No. 1993-283105). However, the thin battery has an energycapacity of 10 Wh or smaller that is too small as a secondary batteryfor a energy storage system.

[0007] Japanese Unexamined Patent Publication Nos. 1982-208079 and1988-24555 propose the use of graphite as a negative-electrode materialfor a lithium secondary battery which is superior in flexibility and onwhich mossy lithium is not deposited even in the case of repetition of acharge-discharge cycle. Because graphite has a special layer structureand a property of forming an inter-calation compound, it is practicallyused as an electrode material for a secondary battery using theproperty. Moreover, various types of carbon having a low crystallinitysuch as carbon having a disordered layer obtained by thermallydecomposing hydrocarbon in a gaseous phase and a selective orientationproperty ar disclosed in Japanese Unexamined Patent Publication No.1988-24555 as materials in each of which an electrolyte is not easily dcomposed.

[0008] These negative-electrode materials have advantages anddisadvantages. When using carbon having a high crystallinity such asgraphite as a negative-electrode material, it is theoretically knownthat a change of potentials due to discharge of lithium ions isdecreased and a capacity to be used for a battery increases. However,when the crystallinity of the carbon is increased, the charging rate islowered probably due to decomposition of an electrolyte, and the carbonis broken due to expansion/contraction of the plane interval of crystalcaused by repetition of charge and discharge.

[0009] Moreover, when using carbon having a low crystallinity as anegative-electrode material, a change of potentials due to discharge oflithium ions increases and thereby, a capacity usable for a batterydecreases, and thus, it is difficult to manufacture a battery having alarge capacity.

[0010] Japanese Unexamined Patent Publication No. 1992-368778 shows thatit is possible to prevent carbon from being broken by forming a doublestructure in which a carbon particle having a high crystallinity iscovered with carbon having a low crystallinity. When using carbonprepared by the above method as an active material, it is theoreticallypossible to obtain an electrode superior in potential smoothness andhaving a large capacity by preventing decomposition of an electrolyte.When attempting formation of a practical electrode by using thedouble-structure active-material particles, an electrode having athickness of 50 to 500 m for a cylindrical battery by applying an activematerial onto copp r foil. However, the capacity p r electrode volum wasnot increased because the electrode density was not easily raised. Morespecifically, it is difficult to raise the electrode density. If settingthe electrode density to 1.20 g/cm³ or more through pressurecompression, a high volume capacity of 400 mAh/cm³ or more of thenegative electrode cannot be resultantly obtained because thedouble-structure active material particles are broken.

[0011] In the case of a large lithium secondary battery (energy capacityof 30 Wh or larger) for an energy storage system, a high energy densitycan be obtained. However, because the design of the battery is generallysimilar to the small battery for a portable devise, a cylindrical orprismatic battery is constituted which has a diameter or a thicknessthree times larger than those of a small battery for a portable devise.In this case, heat is easily stored in the battery due to Joule heatcaused by the internal resistance of the battery in charging ordischarging or internal heat of the battery due to change of the entropyof the active material due to insertion or detachment of lithium ions.Therefore, the difference between the temperature of the inner portionof the battery and the temperature nearby the surface of the batteryincreases and thereby, internal resistances differ. As a result, chargecapacity or voltage is easily fluctuated. Moreover, because two or morebatteries of this type are connected to make a battery module in use,capability of heat storage differs depending on a battery position inthe assembled system and fluctuation of heat storage between batteriesoccurs, and it is difficult to accurat ly control the whole of the battry module. Furthermore, because heat radiation is likely to beinsufficient under high-rate charge/discharge, the battery temperaturerises and thereby the battery is brought under an undesirable state.Therefore, a problem is left in the viewpoint of deterioration ofservice life due to decomposition of an electrolyte, and lack ofreliability, particularly safety, because of the possibility of thermalrunaway of a battery.

[0012] To solve the above problem, in the case of a energy storagesystem for an electric vehicle, the following methods are disclosed: aircooling using a cooling fan, a cooling method using a Peltier element(Japanese Unexamined Patent Publication No. 1996-148189) and a methodfor packing a latent-heat storing material into a battery (JapaneseUnexamined Patent Publication No. 1997-219213). However, these methodsuse external cooling and therefore do not provide essential solution tothe problems.

[0013] Moreover, to obtain a high-capacity battery, it is desirable toset a utilization factor of graphite-based particles used for a negativeelectrode to a value as high as possible. However, when improving theutilization factor, electrodeposition of lithium metal on a negativeelectrode increases and heat produced due to a reaction of anelectrolyte at approximately 150 degree in Celsius increases.Particularly, in the case of a large scale battery, a negative electrodehaving a higher capacity is requested in order to improve the energydensity and safety of the battery.

[0014] Furthermore, a separator having a thickness of 0.02 to 0.05 mmreferred to as a micro-porous film made of polypropylene or polyethyleneused for a commercially available lithium-ion secondary battery is atypical separator for the above lithium battery and it is locallyattempted to use non-woven fabric of the above material for a separator.

[0015] In the case of a flat battery, the front and back surface areasof the battery increase as the thickness of the battery decreases, andholding force to be incurred on the surfaces of the electrodes in thebattery decreases. Particularly, in the case of a large lithiumsecondary battery (energy capacity of 30 Wh or larger) used for a energystorage system, the above phenomenon is remarcable. For example, in thecase of a 100 Wh-class lithium ion battery having a thickness of 6 mm,the front and back surface areas of the battery reach a very large valueof 600 cm² (either side).

[0016] Therefore, when using the above separator for a flat batteryhaving a small holding force for pressing the surface of the electrodes,a problem is left that cyclic deterioration is accelerated due to therepetition of charge and discharge.

[0017] Moreover, as internal structure of a general battery, positiveand negative electrodes and a separator for separating the electrodesfrom each other are layered. In the case of a lithium ion battery, apositive electrode made of metal oxide such as LiCoO₂, a negativeelectrode made of carbon, such as graphite, which can be doped andundoped with lithium, and a separator referred to as micro-porous filmmade of polypropylene, polyethylene or the like and having a thicknessof 0.02 to 0.05 mm are different from each other in dimension. Forexample, in the case of positive and negative electrodes, the negativeelectrode is designed so that it is slightly larg r than the positiveelectrode to prevent electrodeposition of lithium metal on the negativeelectrode and to prevent fluctuation of the products even if facedpositive and negative electrodes are slightly shifted from each otherwhen a battery is assembled. Moreover, the separator is designed so thatit is larger than the positive and negative electrodes in order toprevent a short circuit.

[0018] In the case of a cylindrical battery, positioning of the positiveand negative electrodes and separators different from each other in sizecan be easily contrived in the operation of a winder. However, whenstacking electrodes in a prismatic or box-shaped battery, thepositioning is difficult. Therefore, in such cases, layered electrodesare made by pressing electrodes wound into an ellipse configuration, orby layering electrodes after inserting them into a baggy separator.However, a stacking method having a high packing efficiency of layers isdesired.

[0019] Particularly, in the case of a flat battery, when using themethod of pressing wound electrodes, a short circuit occurs due toseparation of an electrode active-material layer from a current currentcollector at an electrode portion having a intensively pressedcurvature. When using a baggy separator, sufficient pressure cannot beobtained because of a large electrode area. Therefore, a gap is easilyformed between a separator and an electrode layer due to creases or thelike of the separator, and the internal resistance of the battery easilyincreases. Moreover, the binding margin of the separator increases insize and the packing efficiency of the electrodes decreases, influencingthe capacity design of the battery. In view of the above-describedpoints, a stacking method realizing a high packing efficiency ofelectrodes is not found which is suitable for a large scale battery or aflat large scale battery, simplifies positioning of layers, and hardlycauses a short circuit.

[0020] To control a secondary battery for a energy storage system, inthe case of an aqueous secondary battery such as a lead-acid battery ornickel-cadmium battery or the like, a plurality of single cells areconnected in series to constitute a module and a plurality of modulesare connected in series to constitute an assembly of batteries, in manycases. In these cases, charge and discharge operations are generallycontrolled per modules. By measuring voltage, temperature, current, andresistance of a module, the charge and discharge states and thedeterioration level of a battery are determined, and charge anddischarge are controlled in accordance with the determined results, inmany cases.

[0021] In the case of a lithium ion battery, even a commerciallyavailable small secondary battery is generally controlled on cell bycell basis in a serial module (a module formed by serial connection oftwo cells or more). This is because a lithium ion battery has a largeweak point in overcharge and overdischarge. For example, the safety of acell become unsecured only by an overcharge state of several tens of mV,and overcharge or overdischarge fatally deteriorates a cycle life.

[0022] As described in Japanese Un xamined Patent Publication. Nos.1996-182212 and 1997-28042, a lithium ion battery for a energy storagesystem is also controlled on c ll by cell basis. The single-cell controlis the most advanced art among the battery control methods currentlydisclosed and is partly introduced into aqu ous batteries for an energystorage system.

[0023] In the case of a large secondary battery (energy capacity of 30Wh or larger) for a energy storage system, the capacity, volume, andelectrode area for each single cell are ten times or more as large asthose of a small battery for a portable devise and the fluctuation ofoperational characteristics in a single cell, which is not a largeproblem for a small secondary battery, reaches a level which cannot beignored. Particularly, in the case of a large lithium secondary battery,the fluctuation of operational characteristics in a single cell is largeand greatly influences the safety and reliability similarly to thefluctuation of operational characteristics between single cells of asmall lithium ion battery.

[0024] Specifically, there are many fluctuations to be considered in asingle cell such as electrode deterioration, contact pressure applied toan electrode, and current intensity in a current collector in the singlecell. In the case of the above cylindrical and prismatic batteries(batteries having thickness and diameter three times or more as large asthose of small battery for a portable devise), heat is easily stored inthe batteries because of Joule heat due to the internal resistance ofthe batteries during charge or discharge, or because of internallyproduced heat of the batteries due to entropy change of active materialscaused by insertion and detachment of lithium ion. Th refore, thedifference betwe n the temperature inn r portion of the battery and thetemperature nearby the surface of the battery is large, and thus thinternal resistance showing temperature dependency differs, and thecharge capacity and voltage are likely to fluctuate in a single cell.

[0025] However, because the large lithium secondary battery art of thistype is generally similar to a small lithium ion secondary battery,attempts on battery design and charge and discharge control consideringthe fluctuation in a single cell are not made yet. Such attempts are notapplied to aqueous secondary batteries such as a lead-acid battery,nickel-cadmium secondary battery, nickel-hydrogen secondary battery,which are generally controlled per module.

SUMMARY OF THE INVENTION

[0026] It is a main object of the present invention to provide anon-aqueous secondary battery having a large capacity of 30 Wh or largerand a volume energy density of 180 Wh/l or higher and superior inradiation characteristic and safety.

[0027] It is another object of the present invention to provide a flatnon-aqueous secondary battery which can maintain the superiorcharacteristics during cyclic operation.

[0028] It is still another object of the present invention to provide aflat non-aqueous secondary battery which facilitates the stackedstructure and prevents the formation of a short circuit when the batteryis assembled.

[0029] It is still another object of the present invention to provide as condary battery for a energy storage system superior in reliabilitysuch as safety and cyclic durability, and a method for controlling thesame.

[0030] Other features of the present invention will become more apparentfrom the following description.

[0031] To achieve the above objects, the present invention provides aflat non-aqueous secondary battery comprising positive and negativeelectrodes and a non-aqueous electrolyte containing lithium salt andhaving an energy capacity of 30 Wh or larger and a volume energy densityof 180 Wh/l or higher. It is preferable that this secondary battery isflat and has a thickness of less than 12 mm.

[0032] In the present invention, positive- and negative-electrode activematerials are not limited. However, it is preferable to apply A-, B-,and C-type negative electrodes having the following structures.Particularly, when using manganese oxide compound such as lithiummanganese oxide or the like as a positive-electrode active material, theabove negative electrodes have a high effect as described below.

[0033] (A-Type Negative Electrode)

[0034] Negative electrode formed by using graphite having an averageparticle diameter of 1 to 50 mm as active-material particles, a resin asa binder, and a metal as a current collector and having a porosity of 20to 35%, an electrode density of 1.40 to 1.70 g/cm³, and an capacity ofelectrode of 400 mAh/cm³ or higher.

[0035] (B-Type Negative Electrode)

[0036] Negative electrode comprising as active material double-structuregraphite particl s formed with graphite-based particles and amorphouscarbon layers covering the surface of the graphite-based particles, thegraphite-based particles having (d002) spacing of (002) planes of notmore than 0.34 nm as measured by X-ray wide-angle diffraction method,the amorphous carbon layers having (d002) spacing of (002) planes of0.34 nm or larger.

[0037] (C-Type Negative Electrode)

[0038] Negative electrode comprising as active material a carbonmaterial manufactured by mixing at least one of artificial graphite andnatural graphite with a carbon material having volatile components onthe surface and/or in the inside and heat treatment of the mixture.

[0039] In the present invention, when a secondary battery is providedwith a separator, it is preferable to use A- or B-type separator or aseparator capable of positioning an electrode unit having the followingstructure respectively.

[0040] (A-Type Separator)

[0041] A separator in which when a pressure of 2.5 kg/cm² is applied tothe direction of thickness of the separator, the thickness A of theseparator is not less than 0.02 mm and not more than 0.15 mm and theporosity of the separator is 40% or higher, and when the absolute valueof a change rate of the thickness (mm) of the separator relative to thepressure (kg/cm²) applied to the direction of thickness of the separatoris defined as B (mm/(kg/cm²)), the pressure F which renders B/A=1 is notless than 0.05 kg/cm² and not more than 1 kg/cm².

[0042] (B-Type Separator)

[0043] A separator having a first separator and a second separatordifferent from the first separator, wherein when a pressure of 2.5kg/cm² is applied to the direction of thickness of the separator, thethickness A of the first separator is not less than 0.02 mm and not morethan 0.15 mm and the porosity of the first separator is 40% or higher,and when the absolute value of a change rate of the thickness (mm) ofthe first separator relative to the pressure (kg/cm²) applied to thedirection of thickness of the first separator is defined as B(mm/(kg/cm²)), the pressure F which renders B/A=1 is not less than 0.05kg/cm² and not more than 1 kg/cm², and the second separator is amicro-porous film having a thickness of 0.05 mm or less, a pore diameterof 5 mm or less, and a porosity of 25% or more.

[0044] (Separator Capable of Positioning Electrode Unit)

[0045] A separator bonded with a positive and/or negative electrode.

[0046] The above objects of the present invention are also achieved by asecondary-battery operation control method comprising the steps ofmeasuring operational parameters of at different portions of the batteryand controlling operations of the battery based on the results of themeasurement.

[0047] Furthermore, the above objects of the present invention areachieved by a secondary battery for a energy storage system, comprisingpositive and negative terminals for charge and discharge provided on thebattery case and operation-parameter measuring electrodes extending fromdifferent portions of the battery to the outside of the battery case formeasurement of the operation parameters in the batt ry.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048]FIG. 1 shows a top view and a side view of a non-aqueous secondarybattery of an embodiment of the present invention, which is used for aenergy storage system;

[0049]FIG. 2 shows a side view of stacked electrodes to be stored in thebattery shown in FIG. 1;

[0050]FIG. 3 illustrates a manufacturing method of a conventional smallprismatic battery;

[0051]FIG. 4 illustrates a method for manufacturing the bottom caseshown in FIG. 1;

[0052]FIG. 5 illustrates another method for manufacturing a battery caseof a non-aqueous secondary battery of the present invention;

[0053]FIG. 6 shows an electrode used in an embodiment of a non-aqueoussecondary battery of the present invention;

[0054]FIG. 7 is a graph showing results of measurement of the thicknessof an A-type separator while applying a pressure in the thicknessdirection of the separator;

[0055]FIG. 8 shows a side view and a perspective view of a B-typeseparator;

[0056]FIG. 9 shows a side view and a perspective view of another B-typeseparator;

[0057]FIG. 10 shows a side view of stacked electrodes including a C-typeseparator;

[0058]FIG. 11 shows side views of electrode units including a C-type sparator;

[0059]FIG. 12 is illustrations for explaining an electrode unitincluding a C-type separator;

[0060]FIG. 13 is a perspective view of a secondary battery to be appliedto a control method of the present invention;

[0061]FIG. 14 is a block diagram of a control system of the secondarybattery shown in FIG. 13;

[0062]FIG. 15 shows a front view (a) and a top view (b) of an electrodeof the secondary battery shown in FIG. 13;

[0063]FIG. 16 shows a front view (a) and a top view (b) of a secondarybattery storing electrodes shown in FIG. 15;

[0064]FIG. 17 is an enlarged front view of an stacked electrodes in thesecondary battery shown in FIG. 16;

[0065]FIG. 18 shows a front view (a) and a top view (b) of anotherelectrode for the secondary batteries shown above;

[0066]FIG. 19 is an enlarged front view of stacked electrodes using theelectrode shown in FIG. 18; and

[0067]FIG. 20 is a top view of a secondary battery storing electrodesshown in FIG. 18.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068] A non-aqueous secondary battery of an embodiment of the presentinvention is described below by referring to the accompanying drawings.FIG. 1 shows a top view and a side view of a flat rectangular(notebook-type) non-aqueous secondary battery for a energy storagesystem, and FIG. 2 is a side view of stacked electrodes to be stored inthe battery shown in FIG. 1.

[0069] As shown in FIGS. 1 and 2. the non-aqueous secondary battery ofthis embodiment is provided with a battery case (battery vessel)comprising a upper case 1 and a bottom case 2 and an electrode-stackedbody comprising a plurality of positive electrodes 101 a and negativeelectrodes 101 b and 101 c and a separator 104 stored in the batterycase. In the case of the flat non-aqueous secondary battery of thisembodiment, the positive electrode 101 a and the negative electrode 101b (or the negative electrode 101 c formed at the both sides of thestacked body), for example, are alternately arranged and stacked withthe separator 104 positioned therebetween as shown in FIG. 2. However,the present invention is not limited to the above arrangement. It ispossible to change the number of layers correspondingly to a requiredcapacity etc.

[0070] The positive-electrode current collector of each positiveelectrode 101 a is electrically connected to a positive-electrode tab 3via a positive-electrode tab 103 a and similarly, negative-electrodecurrent collectors of the each negative electrodes 101 b and 101 c areelectrically connected to a negative-eletrode tab 4 via anegative-electrode tab 103 b. The positive-electrode tab 3 andnegative-eletrode tab 4 are mounted on the battery case, that is, theupper case 1 while insulated therefrom The entire circumferences of theupper case 1 and the bottom case 2 are welded at the point A shown bythe enlarged view in FIG. 1. The upper case 1 is provided with a safetyvent 5 for releasing the internal pressure in the battery when thepressure rises. The non-aqueous secondary battery shown in FIGS. 1 and 2has, for example, a length of 300 mm, a width of 210 mm, and a thicknessof 6 mm. A lithium secondary battery using LiMn₂O₄ for the positiveelectrode 101 a and graphite described below for the negative electrodes101 b and 101 c has, for example, an energy capacity of 80 to 100 Wh andit can be used for a energy storage system.

[0071] The non-aqueous secondary battery constituted as described abovecan be used for a household energy storage system (for nighttime powerstorage, co-generation, photovoltaic power generation, or the like) anda energy storage system of an electric vehicle or the like and have alarge capacity and a high energy density. In this case, the energycapacity is preferably kept at 30 Wh or larger, more preferably kept at50 Wh or larger, and the energy density is preferably kept at 180 Wh/lor higher, or more preferably kept at 200 Wh/l or higher. When thebattery has an energy capacity of smaller than 30 Wh or a volume energydensity of lower than 180 Wh/l, it is not preferable to use the batteryfor a energy storage system because the capacity is too low to be usedfor a energy storage system and therefore it is necessary to increasethe numbers of batteries connected in series and in parallel, andmoreover it is difficult to compactly design the battery.

[0072] The thickness of the flat non-aqueous secondary battery of thisembodiment is preferably less than 12 mm, more preferably less than 10mm, and still more preferably less than 8 mm. For the lower limit of thethickness, 2 mm or more is practical when considering the packingefficiency of electrodes and the size of a battery (the area of thebattery surface increases as the thickness thereof decreases in order toobtain the same capacity). When the thickness of the battery becomes 12mm or more, it is difficult to sufficiently release the heat produced inthe battery to the outside or the temperature difference between theinner portion and the vicinity of the surface of the battery increasesand the internal resistance differs and resultantly, fluctuations ofcharge capacity and voltage in the battery increase. Though a specificthickness is properly determined in accordance with the battery capacityand energy density, it is preferable to design the battery at a maximumthickness at which an expected radiation of heat is obtained.

[0073] It is possible to form the front and back surfaces of the flatnon-aqueous secondary battery of this embodiment into various shapessuch as angular shape, circular shape, and elliptic shape, etc. Thetypical angular shape is rectangle. However, it is also possible to formthe front and back surfaces into a polygon such as a triangle orhexagon. Moreover, it is possible to form the battery into a cylindricalshape having a small thickness. In the case of the cylindrical shape,the thickness of the cylinder corresponds the thickness of a batterydescribed above. From the viewpoint of easiness of manufacture, it ispreferable that the front and back surfaces of the flat shape batteryare rectangular and the battery is the notebook type as shown in FIG. 1.

[0074] Next, a method for manufacturing a notebook-shaped battery caseis described regarding a method for manufacturing a battery casecomprising the upper case 1 and the bottom case 2. In general, ahousehold small prismatic battery is approximately 50 mm square and hasa thickness of approx. 6 mm. As shown in FIG. 3, the battery case ismanufactured by las r-welding a bottom case 21 (also serving as anegativ terminal) and a upper case 22. The bottom case 21 is formed bydeep-drawing of a thick plate. The upper case 22 is provided with asafety vent and a positive terminal.

[0075] However, it is difficult to manufacture the notebook-type batteryshown in FIG. 1 by the method same as the case of a small secondarybattery. That is, the bottom case 2 of the battery case is obtained bybending a thin plate having the shape shown in FIG. 4 inward along thebroken line L1 and further bending it outward along the alternate longand short dash line L2, thereafter welding the corner shown by A ordrawing a thin plate (very shallow drawing), and welding the upper case1 on which a terminal and a safety vent are set as shown in FIG. 1.Alternatively, the battery case can be manufactured by bending a thinplate and welding the portion A as shown in FIG. 5 to form a structure13 and further welding lateral lids 11 and 12 to the a structure 13.

[0076] A material for a battery case such as the above thin plate isproperly selected in accordance with the purpose or shape of a battery.Iron, stainless steel, or aluminum is generally and practically usedthough not limited specifically. The thickness of a battery case isproperly determined in accordance with the purpose, shape, or materialof the battery case though not limited specifically. Preferably, thethickness of the portion of 80% or more of the surface area of a battery(thickness of the portion having the largest area constituting a batterycase) is 0.2 mm or more. If the above thickness is less than 0.2 mm, itis not preferable because a strength required to manufactur a batterycannot be obtained. From this point of view, a thickness of 0.3 mm ormore is more pr ferable. Moreover, it is preferable that the thicknessof the above portion is 1 mm or less. A thickness of more than 1 mm isnot preferable because the internal volume of the battery decreases andthereby, a sufficient capacity cannot be obtained or the weightincreases. From this point of view, it is more preferable that thethickness is 0.7 mm or less.

[0077] As described above, by designing the thickness of a non-aqueoussecondary battery to less than 12 mm, when the battery has a largecapacity of e.g. 30 Wh or more and a high energy density of e.g. 180Wh/l, rise of the battery temperature is small even under high-ratecharge/discharge and the battery can have a superior heat radiationcharacteristic. Therefore, heat storage of the battery due to internalheat is reduced, and resultantly it is possible to prevent thermalrunaway of a battery and provide a non-aqueous secondary batterysuperior in reliability and safety.

[0078] A positive-electrode active material of a non-aqueous secondarybattery of the present invention is not limited as long as the materialis a positive-electrode material for lithium batteries. It is possibleto use one of lithium-containing cobalt-based oxides, lithium-containingnickel-based oxides, and lithium-containing manganese-based oxides, or amixture of these substances, or moreover a compound material obtained byadding at least one different-type metal element to these compoundoxides. These materials are preferably used to realize a high-voltagelarge-capacity battery. From the view point of safety, it is preferableto use manganese oxide having a high thermal-decomposition temperature.As the manganese oxide, the following are listed: lithium-containingmanganese oxides such as LiMn₂O₄, a compound material obtained by addingat least one different-type metal element to these compound oxides, andLiMn₂O₄ containing lithium and oxygen more than the theoretical ratio.

[0079] A negative-electrode active material of a non-aqueous secondarybattery of the present invention is not limited as long as the materialis a negative-electrode material for lithium batteries. A material thatcan be doped or undoped with lithium is preferable because reliabilitysuch as safety or cycle life is improved. As materials which can bedoped or undoped with lithium, the following can be used: graphitematerials, carbon-based material, metal oxide such as tin-oxide-basedmaterial or silicon-oxide-based material which are used asnegative-electrode materials of publicly-known lithium ion batteries,and an electrically conducting polymer represented by a polyacenicsemiconductors. Particularly, from the viewpoint of safety, it ispreferable to use a polyacenic substance producing small heat atapproximately 150 degree Celsius or a material containing the polyacenicsubstance.

[0080] As the electrolyte of a non-aqueous secondary battery of thepresent invention, it is possible to use a non-aqueous electrolytecontaining publicly-known lithium salt and the electrolyte is properlyselected in accordance with the condition such as the sort of apositive-electrode material or negative-electrode material or chargevoltage. More specifically, a material is used which is obtained bydissolving lithium salt such as LiPF₆, LiBF₄, or LiClO₄ in one ofpropylene carbonate, ethylene carbonate, diethyl carbonate, dimethylcarbonate, methyl ethyl carbonate, dimethoxyethane, g-butyrolactone,methyl acetate, and methyl formate, or an organic solvent such as amixed solvent of two types of these substances or more. Further, it ispossible to use a gel or solid electrolyte.

[0081] Though the concentration of an electrolyte is not limited, 0.5mol/l to 2 mol/l are generally practical. It is preferable to use theelectrolyte having a moisture of 100 ppm or less.

[0082] The word non-aqueous electrolyte referred to in the descriptionand claims of this application denotes either of non-aqueous electrolyteor organic electrolyte, and either of gel or solid electrolyte.

[0083] Embodiments of a secondary battery (flat non-aqueous secondarybattery having an energy capacity of 30 Wh or more and a volume energydensity of 180 Wh/l or more and a thickness of less than 12 mm) of thepresent invention are shown and further specifically described below.

[0084] [Embodiment 1-1]

[0085] A secondary battery of an embodiment of the present invention wasconstituted as described below.

[0086] (1) A mixture slurry for a positive-electrode was obtained bymixing 100 parts by weight of spinel-type LiMn₂O₄ (made by SEIMICHEMICAL; product No. M063), 10 parts by weight of acetylene black, and5 parts by weight of polyvinylidene fluoride (PVdF) with 100 parts byweight of N-methylpyrrolidone (NMP). The slurry was applied to the bothsides of an aluminum foil having a thickness of 20 mm and dried andthen, pressed to obtain a positive electrode. FIG. 5 is an illustrationof an electrode. In the case of this embodiment, the coating area(W1×W2) of an electrode (101) is 268×178 mm² and slurry is applied tothe both sides of a 20 mm aluminum foil (102) at a thickness of 120 mm.As a result, the electrode thickness t is 260 mm. One of the edgeportions of the current collector extending along the arrow W2 andhaving a width of 1 cm is not coated with the electrode, and a tab 103(aluminum having a thickness of 0.1 mm and a width of 6 mm) is weldedthereto.

[0087] (2) A mixture slurry for a negative-electrode was obtained bymixing 100 parts by weight of graphitized mesocarbon microbeads (MCMB:made by OSAKA GAS CHEMICAL Co., Ltd.; product No. 628) and 10 parts byweight of PVdF with 90 parts by weight of NMP. The slurry was applied tothe both sides of a copper foil having a thickness of 14 mm and dried,and then pressed to obtain a negative electrode. Because the shape ofthe negative electrode is the same as the above positive electrode, thenegative electrode is described by referring to FIG. 5. In the case ofthis embodiment, the coating area (W1×W2) of the electrode (101) is270×180 mm² and the slurry is applied to both sides of the copper foil(102) at a thickness of 80 mm. As a result, the electrode thickness t is174 mm. One of the edge portions of the current collector extendingalong the arrow W2 and having a width of 1 cm is not coated with theelectrode, and a tab 103 (nickel having a thickness of 0.1 mm and awidth of 6 mm) is welded thereto.

[0088] Moreover, the slurry was applied to only one side by the samemethod and a single-sided electrode having a thickness of 94 mm wasformed by the same method except for th application of the slurry. Thesingle-sided electrode is positioned at the outermost side in thestacked electrodes which is described in the following Item (3) (101 cin FIG. 6).

[0089] (3) Ten positive electrodes and eleven negative electrodes(including 2 single-sided electrodes) obtained in the above Item (1)were alternately stacked with a separator 104 (made by TONEN TAPIRUSUCo., Ltd.; made of porous polyethylene) held between each of the layersto form an electrode-stacked body.

[0090] (4) The battery bottom case (designated as 2 in FIG. 1) wasformed by bending a thin plate made of SUS304 having the shape shown inFIG. 3 and a thickness of 0.5 mm inward at the lines L1 and outward atthe lines L2 and then arc-welding the corners A. The upper case(designated as 1 in FIG. 1) of the battery case was also formed with athin plate made of SUS304 having a thickness of 0.5 mm. Terminals 3 and4 (diameter of 6 mm) made of SUS304 and a safety-vent hole (diameter of8 mm) are formed on the upper case 1. The terminals 3 and 4 areinsulated from the upper case 1 by a packing made of polypropylene.

[0091] (5) Each positive terminal 103 a of the electrode-stacked bodymade in the above Item (3) was welded to the tab 3 and each negativeterminal 103 b was welded to the tab 4 through a connection line andthen, the electrode-stacked body was set to the battery bottom case 2and fixed by an insulating tape to laser-weld the overall circumferencealong the edge A in FIG. 1. Thereafter, a solution was made bydissolving LiPF₆ at a concentration of 1 mol/l in a solvent obtained bymixing ethyl ne carbonate and diethyl carbonate at a weight ratio of1:1. Th solution was poured through a safety-vent hole as an electrolyteand the hole was closed with aluminum foil having a thickness of 0.1 mm.

[0092] (6) The formed battery had a size of 300×210 mm² and a thicknessof 6 mm. The battery was charged by a constant-current/constant-voltagecharging for 18 hours, in which the battery was charged up to 4.3 V by acurrent of 3 A and then charged by a constant voltage of 4.3 V. Then,the battery was discharged to 2.0 V by a constant current of 30 A. Thedischarged capacity was 26 Ah, energy capacity was 91 Wh, and volumeenergy density was 240 Wh/l.

[0093] (7) As a result of charging and discharging the battery in athermostatic chamber at 20 degree Celsius by the method described in theabove Item (6), a rise of the battery temperature was hardly observedafter the end of discharge.

COMPARATIVE EXAMPLE 1-1

[0094] (1) A battery was constituted similarly to the case of the aboveembodiment except for changeing electrode sizes, numbers of electrodesto be stacked, and battery sizes. In Table 1, the electrode size denotesthe size of the negative electrode. The size of the positiveelectrode is2 mm smaller than the negative electrode size in each side. The numberof electrodes to be stacked denotes the number of positive electrodes.The number of negative electrodes is one more than the number ofpositive electrodes as described for the embodiment 1-1, in which twosingle-side-coated electrod s are included.

[0095] An energy capacity was measured by the same method as Item (6) ofthe embodiment. As a result of performing discharge by the same methodas Item (7) of the embodiment and measuring the surface temperature ofthe battery, discharge was stopped for safety because the temperaturewas greatly raised during the discharge.

[0096] Electrode size (W1×W2): 110×170 (mm)

[0097] Number of electrodes to be stacked: 26

[0098] Battery size: 140×200×40 (mm)

[0099] Energy capacity: 85 (Wh)

[0100] Energy density: 217 (Wh/l)

[0101] Even in the case of the embodiment battery having a batteryenergy capacity of approximately 90 Wh, the battery surface temperaturehardly rose when the battery thickness was less than 12 mm. However, thecomparative example having a thickness of 14 mm showed a highsurface-temperature rise. Therefore, it is clear that theorganic-electrolyte battery of the present invention shows a smalltemperature rise even if the battery is quickly discharged and has ahigh safety.

[0102] [Preferable Negative Electrode Used for Secondary Battery of thePresent Invention]

[0103] In general, lithium-containing manganese oxide used for anon-aqueous secondary battery is a positive-electrode material suitablefor a large scale battery. It is reported that a high-safety battery isobtained by using the lithium manganese oxide for a positive electrodecompared with lithium cobalt oxide and lithium-containing nickel oxide(Like Xi et al., Mat. Res. Soc. Symp. Proc., Vol. 393, 1995, pp.285-304). The positive-electrode material has a density and a capacitylower than those of lithium-containing cobalt-based oxide andlithium-containing nickel oxide. Therefore, to obtain a large-capacitybattery, it is preferable to use A, B, or C-type negative electrodesdescribed below and thereby improved safety is also expected.

[0104] (A-Type Negative Electrode)

[0105] In the case of preferable graphite to be used for the negativeelectrodes 101 b and 101 c as a negative-electrode active material, the(d002) spacing of (002) planes measured by the X-ray wide-anglediffraction method is normally 0.34 nm or less, preferably 0.3354 to0.3380 nm, or more preferably 0.3354 to 0.3360 nm. When the planespacing (d002) exceeds 0.34 nm, crystallinity lowers. Therefore, thechange of potentials due to discharge of lithium ions increases and theeffective capacity usable as a battery lowers.

[0106] The following are listed as materials for manufacturing the abovegraphites: cokes such as pitch coke and needle coke, polymers, andcarbon fibers. By baking these materials at a temperature of 1,500 to3,000 degree Celsius in accordance with the conventional method, it ispossible to obtain desired graphite materials. Specifically, graphiteincludes mesophase-pitch-based graphite fiber, graphitized mesocarbonmicrobeads (hereafter referred to as graphitized MCMB),vapor-phase-epitaxial carbon fiber, and graphit whisker. Particularly,because the particles of graphitized MCMB are almost spherical, ahigh-density lectrode to be m ntioned lat r can be easily obtained.

[0107] The particle diameter of the above graphite is preferably 1 to 50mm, more preferably 3 to 40 mm, or still more preferably 5 to 35 mm. Ifthe particle diameter is less than 1 mm, it is impossible to raise theelectrode density. However, if the particle diameter exceeds 50 mm, alarge capacity cannot be obtained because the graphite is broken when anelectrode having a small thickness of approximately 100 mm is pressed toraise the electrode density.

[0108] The negative electrodes 101 b and 101 c are obtained, forexample, by using an organic solvent solution of a resin serving as abinder, applying the above graphite onto a metal member serving as acurrent collector, drying the metal member and pressing it if necessary.When using a resin as a binder, a negative electrode is obtained whichis stable even at a high temperature and has a high adhesiveness with ametal member serving as a current collector.

[0109] The negative electrodes 101 b and 101 c thus obtained and havinga porosity of 20 to 35% and an electrode density of 1.40 to 1.70 g/cm³(more preferably having an electrode density of 1.45 to 1.65 g/cm³,particularly preferably having an electrode density of 1.50 to 1.65g/cm³) are easily impregnated with the electrolyte, in which lithiumions and electrons are smoothly moved. Therefore, it is possible toobtain a negative electrode having a high capacity of electrode of 400mAh/cm³ or more. By using a negative lectrode having a high capacity ofelectrode of 400 mAh/cm³ or more, it is possible to improve the batterycapacity without raising th utilization ratio of a negative-electrodactive mat rial and thus the safety such as prevention of lithium fromelectrodeposition or the like can be easily secured.

[0110] The above resin serving as a binder binds graphite particles eachother and fixes active-material particles on metallic foil. As thebinder resin, the following materials can be used without limitationthereto: fluorinated resins such as polyvinylidene fluoride (PVdF) andpoly-4-ethylene fluoride, fluorine rubber, SBR, acrylic resin, andpolyolefins such as polyethylene and polypropylene. Among them, a resinsoluble in widely used organic solvents (such as N-methylpyrrolidone,toluene, and styrene) and superior in electrolyte resistance andwithstanding high-voltage are preferable, and particularlypolyvinylidene fluoride (PVdF) is preferable.

[0111] A binder mixing quantity in a negative electrode is not limited.It is allowed to properly determine the binder mixing quantity inaccordance with the type, particle diameter, shape, or thickness andstrength of a purposed electrode. However, it is normally preferable toset the binder mixing quantity in a range of 1 to 30% of the weight ofgraphite.

[0112] In this embodiment, as a metal for the current collector copperfoil, stainless-steel foil, or titanium foil can be used withoutlimitation thereto. Moreover, it is possible to use materials allowingan electrode to be formed on metallic foil or between metallicmaterials, such as expand metal or mesh material. Among these materials,it is more pref rable to use a copp r foil having a thickness of 1 to 50mm because it allows a negative electrode to be easily formed by acoating method to be mentioned later and is sup rior in strength andelectric resistance.

[0113] A method of using polyvinylidene fluoride (PVdF) as a binderresin and a copper foil as a current collector is described below as aspecific method for manufacturing the negative electrode for anon-aqueous secondary battery of this embodiment having a high capacityof electrode of 400 mAh/cm³. It is needless to say that methods formanufacturing the negative electrode of this embodiment are not limitedto the method.

[0114] First, a slurry is prepared by uniformly dissolving graphite in abinder-resin solution obtained by dissolving polyvinylidene fluoride(PVdF) in N-methylpyrrolidone. In this case, it is also possible to adda conductive material such as acetylene black or binder assistant suchas polyvinyl pyrrolidone. Then, the obtained slurry is applied ontocopper foil by a coater and dried, and an electrode layer is formed onthe copper foil, and then pressed to obtain a negative electrode for thenon-aqueous secondary battery, which has a thickness of 50 to 500 mm.The electrode layer is formed on both sides or either side of the copperfoil according to necessity.

[0115] The negative electrode thus obtained is a high-density electrodewhose capacity is hardly lowered and having a density of 1.40 to 1.70g/cm³, preferably having a density of 1.45 to 1.65 g/cm³, or morepreferably having a density of 1.50 to 1.65 g/cm³, a porosity of 20 to35%, and an capacity of electrode of 400 mAh/cm³ or more. The densityand porosity are values of an electrode layer formed on metallic foil,which can be calculated in accordance with the true densities of thegraphite and binder resin in the electrode layers and the electrodedensity. The capacity of electrode is a capacity expressed on the basisof the volume of electrode layers.

[0116] (B-Type Negative Electrode)

[0117] A graphite-based particle used for the negative electrodes 101 band 101 c as a negative-electrode active material has a double structureobtained by covering the surface of a graphite particle with amorphouscarbon. By using the double-structure graphite-based particle,deterioration of charge rate probably due to decomposition ofelectrolyte is substantially prevented and a graphite structure isprevented from breaking.

[0118] In the negative electrodes 101 b and 101 c, the (d002) spacing of(002) planes of a graphite-based particle used as an active material isnormally 0.34 nm or less, more preferably 0.3354 to 0.3380 nm, and stillmore preferably 0.3354 to 0.3360 nm as measured by the X-ray wide-anglediffraction method. When the plane interval exceeds 0.34 nm,crystallinity lowers and thereby, the change of potentials due todischarge of lithium ions increases and the effective capacity usable asa battery lowers.

[0119] The plane spacing of amorphous carbon layers coating thegraphite-based particles is such that the (d002) spacing of (002) planesis 0.34 nm or more, preferably about 0.34 to 0.38 nm, more preferablyabout 0.34 to 0.36 nm as measured by the X-ray wide-angle diffractionmethod. When this value is below 0.34 nm, crystallinity is too large,and thereby, charging rate lowers probably due to decomposition of elctrolyte, and carbon material is broken du to increase/decrease of theplane distance with repeated charging and discharging. On the otherhand, when this value exceeds 0.38, the displacement of lithium ions isrestricted and thus the effective capacity usable as a battery lowers.

[0120] Materials for manufacturing the above graphite-based particlesinclude cokes such as pitch coke and needle coke, polymers, and carbonfibers. By baking these materials in accordance with the conventionalmethod at a temperature of 1,500 degree Celsius to 3,000 degree Celsius,desired graphite-based particles can be obtained.

[0121] As materials for forming a covering layer of graphite particle,organic materials such as pitches and polymers can be used. Amorphouscarbon for the covering layer can be obtained by covering the surface ofthe graphite-based particle material obtained in accordance with theabove method with a liquid organic material (such as melted pitch) andbaking the covering organic material at a temperature of 500 degreeCelsius to 2,000 degree Celsius to carbonize it.

[0122] Furthermore, the above double-structure graphite-based particleshave a high capacity per weight of 350 mAh/g and achieve a high initialefficiency of 90% or more. Therefore, it is possible to improve thebattery capacity without raising the utilization ratio of anegative-electrode active material and thereby, the safety such asprevention of lithium from electrodeposition can be easily secured.

[0123] The diameter of a double-structure active-material particlecomprising the above graphite-based particle and its covering layer ispreferably 1 to 50 mm, more preferably 3 to 40 mm, and still morepreferably 5 to 35 mm. When the particle diameter of thedouble-structure body is less than 1 mm, it is impossible to improve theelectrode density. When the particle diameter exceeds 50 mm, a largecapacity cannot be obtained because a double-structure active-materialparticle is broken when an electrode having a small thickness of 100 mmis pressed to raise an electrode density.

[0124] The negative electrodes 101 b and 101 c are obtained by using anorganic solvent solution of a resin serving as a binder, therebyapplying the above double-structure active-material particles onto ametal serving as a current collector, drying them, and pressing them ifnecessary. When using a resin as a binder, a negative electrode isobtained which is stable even at a high temperature and has highadhesiveness with a metal member serving as a current collector.

[0125] The negative electrodes 101 b and 101 c obtained as describedabove and having a porosity of 20 to 35%, an electrode density of 1.20to 1.60 g/cm³ (more preferably having a porosity of 1.35 to 1.60 g/cm³or particularly preferably having a porosity of 1.40 to 1.60 g/cm³) areeasily impregnated with electrolyte, in which lithium ions and electronsare smoothly moved. Therefore, it is possible to obtain a negativeelectrode having a high capacity of electrode of 400 mAh/cm³ or more. Anegative electrode having a high capacity of electrode of 400 mAh/cm³ ormore is more effective used in view of the capacity and safety of abattery as described below.

[0126] The above resin serving as a binder binds double-structureactive-material particles each other and fixes active-material particleson the metallic foil. As binder resins the following materials can beused without limitation thereto: fluorinated resins such aspolyvinylidene fluoride (PVdF) and poly-4-ethylene fluoride, fluorinerubber, SBR, acrylic resin, and polyolefins such as polyethylene orpolypropylene. Among them, a resin soluble in widely used organicsolvents (such as N-methylpyrrolidone, toluene, and styrene) andsuperior in electrolyte resistance and withstanding high-voltage ispreferable, and particularly polyvinylidene fluoride (PVdF) ispreferable.

[0127] A binder mixing quantity in a negative electrode is not limited.It is allowed to properly determine the binder mixing quantity inaccordance with the type, particle diameter, shape, or thickness andstrength of a purposed electrode. However, it is normally preferable toset the binder mixing quantity in a range of 1 to 30% of the weight ofactive-material particles.

[0128] In this embodiment, as a metal for current collector a copperfoil, stainless-steel foil, or titanium foil can be used withoutlimitation thereto. Moreover, it is possible to use materials allowingan electrode to be formed on a metallic foil or between metallicmaterials, such as expand metal or steel. Among these materials, it ismore preferable to use a copper foil having a thickness of 1 to 50 mmbecause it allows a negative electrode to be easily formed by a coatingmethod to be mentioned later and is superior in strength and electricresistance.

[0129] A method of using polyvinylid ne fluoride (PVdF) as a binderresin and a copper foil as a current collector is described below as aspecific method for manufacturing the negative electrode for anon-aqueous secondary battery of this embodiment having a high capacityof electrode of 400 mAh/cm³. It is needless to say that methods formanufacturing the negative electrode of this embodiment are not limitedto the above method.

[0130] First, a slurry is prepared by uniformly dissolvingdouble-structure active-material particles in a binder-resin solutionobtained by dissolving polyvinylidene fluoride (PVdF) inN-methylpyrrolidone. In this case, it is also possible to add aconductive material such as acetylene black or binder assistant such aspolyvinyl pyrrolidone. Then, the obtained slurry is applied onto acopper foil by a coater and dried, and an electrode layer is formed onthe copper foil, and then pressed to obtain a negative electrode for thenon-aqueous secondary battery, which has a thickness of 50 to 500 mm.The electrode layer is formed on both sides or either side of the copperfoil according to necessity.

[0131] To manufacture a negative electrode, it is necessary to preventgraphite from breaking. For example, in the case of the abovemanufacturing example, it is necessary to pay attention to variousconditions in the pressing step. Specifically, the following can belisted as these conditions: a pressing rate, tension, and rollercurvature for pressing an electrode layer formed on a metallic foil byrollers, a dried state (remaining amount of solvent) of the electrodelayer before pressing, and a pressing temperature.

[0132] It is desirable to control a dried level (remaining amount ofsolvent) of an electrod layer before pressed normally at 1 to 10%,preferably at 1 to 8%, and still more preferably at 2 to 5%. When theseamounts of solvent remain, it is possible to improve an electrode-layerdensity by pressing without breaking graphite. That is, when a certainamount of solvent remains, the solvent is present on surfaces ofgraphite, binder, and conductive material, which supposedly improvesslippage between these materials during the pressing step andresultantly an electrode-layer density can be improved without breakinggraphite material.

[0133] In the conventional common sense, a solvent is regarded as animpurity and it has been considered that a remaining amount of thesolvent should be minimized (a remaining amount of the solvent should bekept at 0.2% or less). However, according to the study of the presentinventor, when controlling a remaining amount of solvent within apredetermined range, negative electrode for a nonaqueous secondarybattery having a high electrode density and a large capacity can beobtained compared with the case of a conventional method.

[0134] An electrode-layer pressing temperature is normally kept atordinary temperature (25 degree Celsius) to 140 degree Celsius,preferably kept at ordinary temperature to 100 degree Celsius, or morepreferably kept at ordinary temperature to 70 degree Celsius.

[0135] By previously adjusting the above conditions (particularly, aremaining amount of a solvent) on trial, it is possible to manufacturean electrode without breaking graphite, that is, an electrode can bemanufactured without lowering the capacity even if the density of theelectrode is raised.

[0136] The negative electrode thus obtained is a high-density electrodewhose capacity is hardly lowered and having a density of 1.20 to 1.60g/cm³, preferably having a density of 1.35 to 1.60 g/cm³, or morepreferably having a density of 1.40 to 1.50 g/cm³, a porosity of 20 to35%, and an capacity of electrode of 400 mAh/cm³ or more. The densityand porosity are values of an electrode formed on metallic foil, whichcan be calculated in accordance with true densities of double-structureactive-material particles and a binder resin and the electrode densityin the electrode layer. Also, the capacity of electrode is a capacityexpressed on the basis of the volume of electrode layers.

[0137] (C-Type Negative Electrode)

[0138] The negative-electrode active material used for the negativeelectrodes 101 b and 101 c can be manufactured using carbon (hereafterreferred to as “coating graphite”) which is obtained by mixing at leasteither of artificial graphite or natural graphite with carbon having avolatile component on the surface and/or inside thereof (hereafterreferred to as “volatile-component-contained carbon”) and then bakingthem. The active material thus manufactured is substantially preventedfrom deterioration of the charge rate probably due to decomposition ofelectrolyte does not substantially occur and a graphite structure isalso prevented from breaking.

[0139] The coating graphite has a structure in which a volatilecomponent derived from a volatile-component-contained carbon attaches atleast a part of artificial graphite and/or natural graphite by baking amixed material or covers at least a part of artificial graphite and/ornatural graphite. It is presumed that the above attaching structure orcovering structure is formed when the volatile component of thevolatile-component-contained carbon once vaporizes and then attaches apart or the whole of the artificial graphite and/or natural graphite orcovers a part or the whole of the artificial graphite and/or naturalgraphite. In other words, it is presumed that a part or the whole of theartificial graphite and/or natural graphite is covered in a gaseousphase.

[0140] In general, artificial graphite and natural graphite serving asnegative-electrode materials have a problem of damaging the stability ofthe electrolyte because they respectively have a large specific surfacearea though they respectively have a large capacity usable as a battery.However, to cover artificial graphite or natural graphite in a gaseousphase, it is presumed that the covering thickness is very small anduniform. As a result, it is possible to substantially decrease thespecific surface area of artificial graphite or natural graphite withoutsubstantially lowering a large capacity of the artificial graphite ornatural graphite and therefore, it is presumed that high-capacitycoating graphite can be obtained.

[0141] It is possible to form coating graphite in a liquid phase. Thatis, by soaking graphite serving as a core material in liquid-phase“carbon for forming a coat”, it is possible to obtain coating graphite.Also in this case, by d creasing a ratio of [coat-forming volatilecomponent]/[core material+coat-forming volatile component] (this ratiois h reafter referred to as “coating ratio”), it is expected thathigher-capacity carbon may be obtained similarly to the case of thegaseous phase. Actually, however, forming a thin covering layer in aliquid phage is not suitable, because a problem occurs that the coveringlayer is separated from a core material or the covering layer is lackingin uniformity and the specific surface area of coating graphiteincreases.

[0142] As volatile-component-contained carbon used for this embodiment,the following can be listed: carbon (volatile-component-containedcarbon) serving as a core material a part or the whole of which iscovered with coat-forming volatile component (such as coal tar pitch),mesocarbon micro beads, carbon fiber, mesophase pitch, isotropic pitch,resin, and a mixture of these materials. Among them, thevolatile-component-contained carbon is preferable from the viewpoint ofcost. It is preferable that the coating ratio of thevolatile-component-contained carbon is 0.01 or more, it is morepreferable that the ratio is 0.05 or more, or it is still morepreferable that the ratio is not less than 0.05 and not more than 0.3.

[0143] If the coating ratio of the volatile-component-contained carbonis too low, the carbon does not sufficiently cover or attach a part orthe whole of artificial graphite and/or natural graphite because theamount of a volatile component to be evaporated is small when thematerial is baked while mixed with artificial graphite and/or naturalgraphite. However, if the coating ratio is too large, it is difficult toobtain a sufficient capacity because the capacity of a low-potentialportion dep nding on a core material lowers when a battery ismanufactured. The amount of the “volatile component” was determined bythe following: A carbon component derived from heavy oil covering thecircumference of carbon serving as a core material was solvent-analyzedin accordance with the method specified in JIS K2423. Firstly, aquinoline component (%) was measured and then {100-(quinolinecomponent)} was defined as a quinoline soluble component (%). Thequinoline soluble component is the above “amount of coat-formingvolatile component” and the above “coating ratio” can be calculated byusing the amount of coat-forming volatile component and the carbonserving as a core material.

[0144] Volatile-component-contained carbon in which a part or the wholeof carbon serving as a core material is covered with a volatilecomponent is manufactured as described below. That is, carbon particlesserving as a core material is soaked in coal-based or oil-based heavyoil such as tar or pitch preferably at 10 to 300 degree Celsius toseparate the carbon from the heavy oil, and then an organic solvent isadded to the separated carbon to clean them preferably at 10 to 300degree Celsius. By properly adjusting the mixed ratio between the carbonparticles and the heavy oil, it is possible to omit the above cleaningstep. However, it is preferable to execute the cleaning step. Whenomitting the cleaning step, a problem may occur that particles of thevolatile-component-contained carbon adhere or cohere each other whenbaked or the volatile component does not uniformly attach or cover thecore material. Moreover, when manufacturing volatile-component-containedcarbon while soaking carbon in heavy oil at a temperature exceeding 300degree Celsius and accelerating the polycondensation of h avy oil, thesame problem may occur. Furthermore, it is possible to perform thebaking step at 300 to 600 degree Celsius instead of the above cleaningstep. In this case, however, volatile-component-contained carbon doesnot uniformly attach or cover a core material though particles do noteasily adhere or cohere each other.

[0145] To manufacture volatile-component-contained carbon, a mechanicalstirring method using a nauta mixer, ribbon mixer, screw-type kneader,or widely used mixer is used as a method for mixing carbon particleswith heavy oil.

[0146] Though the mixing ratio between artificial graphite and/ornatural graphite and volatile-component-contained carbon mainly dependson the amount of the volatile component of the carbon, it is normally 10to 1,000 parts by weight of artificial graphite and/or natural graphite,more preferably 10 to 300 parts by weight of artificial graphite and/ornatural graphite, still more preferably 30 to 100 parts by weight ofartificial graphite and/or natural graphite, to 100 parts by weight ofthe volatile-component-contained carbon. When the amount of artificialgraphite and/or natural graphite is too small, the ratio of thecoating-graphite component that should serve as a higher capacity partin carbon for a battery lowers and thereby, the capacity is notsufficiently raised. However, when the amount of artificial graphiteand/or natural graphite is too large, the amount of a volatile componentto be evaporated when baking a mixture relatively decreases. Therefore,artificial graphite and/or natural graphite is not sufficiently coveredand a desired specific surface area of carbon increases.

[0147] A mixture of artificial graphite and/or natural graphite andvolatile-component-contained carbon is baked in a reducing atmosphere orinert gas flow, or a non-oxidation atmosphere such as a closed statecontaining an inert gas or vacuum state. Because the mixture is baked inorder to cover a part or the whole of artificial graphite and/or naturalgraphite by evaporating a volatile component in multilayer carbon in agaseous phase, it is more preferable to bake the mixture in anatmosphere in which the volatile component ofvolatile-component-contained carbon easily stays, that is, in a reducingatmosphere or inert-gas contained state. Carbonization in a vacuum statehas an effect of removing a surface functional group of carbon and anadvantage that retention can be reduced but has a disadvantage that avolatile component is easily lost from the volatile-component-containedcarbon.

[0148] The above mixture is baked to be carbonized normally at atemperature of about 600 degree Celsius to 2,000 degree Celsius, andmore preferably at a temperature of 900 degree Celsius to 1,300 degreeCelsius. The above mixture is baked to be graphitized normally at atemperature of about 2,000 degree Celsius to 3,000 degree Celsius, morepreferably at a temperature of about 2,500 degree Celsius to 3,000degree Celsius. An ungraphitized part may remain in a baked productdepending on a mixture baking condition and the remaining ungraphitizedpart may slightly influence the characteristic of a negative electrode.However, this does not substantially matter. However, to further improvethe negative-electrode characteristics, it is more preferable to usegraphite as a core material of volatile-component-contained carbon orfurther improve the graphitization degree of a baked product by bakingat a higher temperature.

[0149] It is possible to select a temperature-rise rate when baking amixture from a range of 1 to 300 degree Celsius/hr at any bakingtemperature. The baking time ranges between 6 hours and one month.

[0150] The particle diameter of coating graphite used as anegative-electrode active material in this embodiment is normally 1 to50 mm, more preferably 3 to 40 mm, and still more preferably 5 to 35 mm.When the particle diameter of the coating graphite is too small, it isimpossible to raise an electrode density, However, when the particlediameter is too large, a large capacity is not obtained becausecovering-graphite particles are broken when performing pressing to raisean electrode density in order to manufacture a thin electrode having athickness of approximately 100 mm.

[0151] The negative electrodes 101 b and 101 c are obtained by using anorganic solvent solution of a resin serving as a binder, applying thecoating-graphite particles onto a metal member serving as a currentcollector, drying them, and pressing them if necessary. When using aresin as a binder, a negative electrode is obtained which is stable evenat a high temperature and has a high adhesiveness with a metal memberserving as a current collector.

[0152] The negative electrodes 101 b and 101 c thus obtained and havinga density of 1.20 to 1.60 g/cm³ (more preferably having a density of1.35 to 1.60 g/cm³) and a porosity of 20 to 35% are easily impregnatedwith electrolyte, in which lithium ions and electrons are smoothlymoved. Therefore, it is possible to obtain a negative electrode having ahigh capacity of electrode of 400 mAh/cm³ or more. Use of the negativeelectrode having a high capacity of electrode of 400 mAh/cm³ or more ismore effective for the battery capacity and safety described below.

[0153] The above resin serving as a binder binds coating-graphiteparticles each other and binds and fixes active-material particles ontometallic foil. As resins serving as binders the following can be usedwithout limitation thereto: fluorinated resins such as polyvinylidenefluoride (PVdF) and poly-4-ethylene fluoride, fluorine rubber, SBR,acrylic resin, and polyolefins such as polyethylene and polypropylene.Among these materials, a material is preferable which is particularlysoluble in organic solvents for general purposes (such asN-methylpyrrolidone, toluene, and styrene) and superior in electrolyteresistance and withstanding a high-voltage. For example, polyvinylidenefluoride (PVdF) is preferable.

[0154] A binder mixing quantity is not limited. It is allowed toproperly determine a binder mixing quantity for a negative electrode inaccordance with the type, particle diameter, shape, purposed electrodethickness, or strength of a coating-graphite particle. However, it isnormally preferable to use a rate of 1 to 30% of the weight ofactive-material particles.

[0155] In this embodiment, as a metal used as a current collector acopper foil, stainless-steel foil, or titanium foil can be used withoutlimitation thereto. It is possible to use a metal allowing an lectrodeto be formed on metallic foil or between metal materials such as expandmetal or ste 1. Among them, copper foil having a thickness of 1 to 50 mmis more preferable because the foil allows a negative electrode to beeasily manufactured in accordance with the coating method to bedescribed later and is superior in strength and electric resistance.

[0156] A method of using polyvinylidene fluoride (PVdF) as a binderresin and copper foil as a current collector is described below as aspecific method for manufacturing the negative electrode for anon-aqueous secondary battery of this embodiment having a high capacityof electrode of 400 mAh/cm³. It is needless to say that methods formanufacturing the negative electrode of this embodiment are not limitedto the above method.

[0157] First, a slurry is prepared by uniformly dissolving coatinggraphite in a binder-resin solution obtained by dissolvingpolyvinylidene fluoride (PVdF) in N-methylpyrrolidone. In this stage, itis also possible to add a conductive material such as acetylene black orbinder assistant such as polyvinyl pyrrolidone. Then, the obtainedslurry is applied onto copper foil by a coater and dried, and anelectrode layer is formed on the copper foil, and then pressed to obtaina negative electrode having a thickness of 50 to 500 mm for thenon-aqueous secondary battery. The electrode layer is formed on bothsides or either side of the copper foil according to necessity.

[0158] The negative electrode thus obtained is a high-density electrodehaving a density of 1.20 to 1.60 g/cm³ (more preferably having a densityof 1.35 to 1.60 g/cm³) and an capacity of electrode of 400 mAh/cm³ ormore, but hardly lowering a capacity. The density and porosity arevalues of an electrode layer formed on metallic foil, which can becalculated in accordance with coating-graphite particles in an electrodeand the true density of a binder resin, and an electrode density. Thecapacity of electrode is a capacity expressed on the basis of the volumeof electrode layers.

[0159] When densities of A-, B, and C-type negative electrodes are toolow, a sufficient capacity of electrode cannot be obtained. However,when the densities are too high, this is not preferable because acapacity is lowered due to breakdown of graphite. When a porosity is toolow, a sufficient rate characteristic is not obtained. However, when theporosity is too high, a sufficient capacity of electrode is notobtained.

[0160] The above “capacity of electrode” is a capacity of an electrodedefined by sufficiently doping and dedoping lithium. For example, thededoping capacity is measured by assembling electrochemical cells usinga lithium metal as an counter electrode and a reference electrode,incurring a constant voltage to the counter electrode at a potential of1 mV vs. the lithium-metal potential in a non-aqueous electrolyte to bementioned later, doping the lithium until a current value becomes smallenough (e.g. 0.01 mA/cm²), then dedoping the lithium up to 2 V relativeto the lithium potential at a sufficiently slow rate (e.g. 0.25 mA/cm²).By dividing the dedoping capacity by an electrode volume, the capacityof electrode referred to in the present invention is obtained. Now, thedescription of each of the A, B, and C-type negative electrodes iscompleted.

[0161] The present invention is further specifically described belowwith the reference to an embodiment of each of the A, B, and C-typenegative electrodes.

[0162] [A-Type Negative Electrode]

[0163] (Embodiment 2-1)

[0164] (1) A positive-electrode mixture slurry was obtained by mixing100 parts by weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL,product No. M063), 10 parts by weight of acetylene black, and 5 parts byweight of polyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of aluminum foil having a thickness of 20 mmand serving as a current collector, and by drying and pressing the foil.FIG. 6 is an illustration of an electrode. In the case of thisembodiment, the coating area (W1×W2) of an electrode 101 was 268×178 mm²and the slurry was applied to both sides of a current collector 102 of20 mm thickness at a thickness of 128 mm. As a result, the electrodethickness t was 276 mm. One of the edge portions of the shorter side ofthe current collector 102 was not coated in 1 cm width and a tab 103(aluminum with a thickness of 0.1 mm and a width of 6 mm) was welded.

[0165] (2) A negative-electrode slurry was obtained by mixing 100 partsby weight of graphitized mesocarbon microbeads (MCMB, made by OSAKA GASCHEMICAL, product No. 6-28) and 10 parts by weight of PVdF with 90 partsby weight of NMP. A negative electrode was obtained by applying theslurry to both sides of a copper foil having a thickness of 14 m andserving as a current collector, and by drying and then pressing thefoil. Before pressing the foil, 4.3% of NMP was left in the electrode.The electrode density was 1.58 g/cm³, and previous evaluation of thecapacity of electrode of the electrode was 430 mAh/cm³. Because theshape of the electrode was the same as that of the above-describedpositive electrode, the negative electrode is described below withreference to FIG. 6. In the case of this embodiment, the coating area(W1×W2) of the electrode 101 was 270×180 mm² and the slurry was appliedto both sides of the current collector 102 of 14 mm thickness at athickness of 72 mm. As a result, the electrode thickness t was 158 mm.One of the edge portions of the shorter side of the current collector102 was not coated in 1 cm width and a tab 103 (nickel with a thicknessof 0.1 mm and a width of 6 mm) was welded.

[0166] The slurry was applied to only one side by the same method and asingle-sided electrode having a thickness of 86 mm was formed by thesame method except for the application of the slurry. The single-sidedelectrode was positioned at the outermost in the stacked electrodesdescribed in Item (3) (101 c in FIG. 2).

[0167] (3) An electrode-stacked body was formed by alternately stacking10 positive electrodes and 11 negative electrodes (including twosingle-sided electrodes) obtained in the above Item (1) with a separator104 (made by TONEN TAPIRUSU, porous polyethylene) held between each ofthe layers.

[0168] (4) The bottom case 2 of the battery (refer to FIG. 1) was formedby bending a thin plate made of SUS304 having the shape shown in FIG. 4and a thickness of 0.5 mm inward along the broken lines L1 and moreoverbending the thin plate outward along the alternate long and short dashlines L2, thereafter arc-welding the corners A. The upper case 1 of thebattery was formed of a thin plate made of SUS304 having a thickness of0.5 mm. A positive electrode and a negative electrode 3 and 0.4 made ofSUS304 (diameter of 6 mm) and a safety-vent hole (diameter of 8 mm) wereformed on the upper case 1, and the positive and negative electrodes 3and 4 were insulated from the upper case 1 by a polypropylene packing.

[0169] (5) Each positive-electrode tab 103 a of the electrode-stackedbody made in the above Item (3) was welded to the positive-electrode tab3 and each negative-electrode tab 103 b was welded to thenegative-eletrode tab 4 through a connection line and then, theelectrode-stacked body was set to the battery bottom case 2 and fixed byan insulating tape to laser-weld the overall circumference along theedge A in FIG. 1. Thereafter, a solution made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1 was pouredthrough a safety-vent hole as electrolyte and the hole was closed byusing an aluminum foil having a thickness of 0.1 mm.

[0170] (6) The formed battery has a size of 300 mm×210 mm×6 mm. Thebattery was charged by a constant-current/constant-voltage charging for18 hours, in which the battery was charged up to 4.3 V by a current of 3A and then charged by a constant voltage of 4.3 V. Then, the battery wasdischarged to 2.0 V by a constant current of 3 A. The discharge capacitywas 27.5 Ah, the energy capacity was 99 Wh, and the volume energydensity was 262 Wh/l.

[0171] (7) As a result of charging the battery and discharging thebattery at a current of 30A in a thermostatic chamber at 20 degreeCelsius by the method described in the above Item (6), rise of thebattery temperature at the end of discharge was small compared with thecase of the assembled prismatic battery (thickness of 12 mm or more)having the same capacity.

COMPARATIVE EXAMPLE 2-1 Comparison With Embodiment 2-1

[0172] A positive electrode was formed which was the same as that of theembodiment 2-1 except that slurry was applied to both sides of a currentcollector 102 at a thickness of 120 mm and the electrode thickness t wasset to 260 mm.

[0173] Then, a negative electrode was obtained by applyingnegative-electrode mixture slurry same as that of the embodiment 2-1 toboth sides of the current collector 102 in a condition different fromthat of the embodiment 2-1, drying the current collector 102, and thenpressing it. Before pressing the current collector 102, 0.2% of NMP wasleft on the electrode. The electrode density was 1.39 g/cm³ and theprevious evaluation of the capacity of electrode of the electrode was372 mAh/cm³. In the case of the comparative example, the coating area(W1×W2) of an electrode 101 is 270×180 mm² and slurry was applied toboth sides of the current collector 102 of 14 mm thickness at athickness of 80 mm. As a result, the electrode thickness t was 174 mm.The only one side was coated in accordance with the same method and asingle-sided electrode of 94 mm thickness was formed formed by the samemethod except for the single-sided coating. Other points were the sameas the case of the embodiment 2-1.

[0174] Thereafte, as a result of forming a battery in accordance withthe same method as the case of the embodim nt 2-1 and measuring thecapacity, it showed 25.8 Ah. The energy capacity was 93 Wh and thevolume energy density was 249 Wh/l that was lower than the case of theembodiment 2-1.

[0175] [B-Type Negative Electrode]

[0176] (Formation of Electrode)

[0177] An electrode was formed by the following materials:double-structure active-material particles used as a negative-electrodeactive material and obtained by covering the surface of graphiteparticles with amorphous carbon, acetylene black (trade name: DENKABLACK; made by DENKIKAGAKU KOGYOU Co., Ltd.) used as a conductivematerial, and a solution used as a binder and obtained by dissolvingpolyvinylidene fluoride (PVDF) (product name: KF#1100; made by KurehaChemical Industry Co., Ltd.) in N-methylpyrrolidone. That is, negativeelectrodes 1 to 7 respectively having a thickness of 100 mm were formedby applying the polyvinylidene fluoride (PVdF) solution to copper foilhaving a thickness of 14 mm serving as a current collector and then,drying the foil at 80 degree Celsius for 15 min, and continuouslypressing the foil by a roller press having a radius of curvature of 30cm while making N-methylpyrrolidone remain.

[0178] An electrode 8 was formed similarly to the case of the electrode1 except for using graphitized MCMB (made by OSAKA GAS CHEMICAL Co.,Ltd.; product No. 6-28).

[0179] Table 1 shows the diameters (mm) of the obtained double-structureactive-material particles and the (d002) spacing of (002) planes of thegraphite particles and its covering carbon layer measur d by the X-raywide-angle diffraction method (unit is nm in both cas). Table 2 showselectrode densities, initial capacities, and remaining amount of solventof the negative electrodes 1 to 8. Mixing ratios of electrode layers are90 wt % of graphite particles and 10 wt % of polyvinylidene fluoride(PVdF). TABLE 1 Graphite Double-structure particle Graphite particleCovering carbon material: No. diameter (μm) (d002) layer (d002) 1 10.335 0.340 2 1 0.335 0.380 3 1 0.337 0.340 4 20 0.335 0.360 5 20 0.3400.380 6 50 0.335 0.340 7 50 0.336 0.380

[0180] TABLE 2 Negative- electrode Electrode Initial Remaining Negativeactive density capacity amount of solvent electrode: No. material(g/cm³) (mAh/cm³) (wt %) 1 No. 1 1.40 435 2.1 2 No. 2 1.45 440 3.4 3 No.3 1.53 465 5.0 4 No. 4 1.60 468 10.0 5 No. 5 1.45 440 1.0 6 No. 6 1.42438 4.8 7 No. 7 1.35 430 2.7 8 MCMB 1.39 370 2.5

[0181] As shown in Tables 1 and 2, the negative electrodes 1 to 7 usingdouble-structure active-material particles respectively have anelectrode density of 1.35 to 1.60 g/cm³ and a capacity of 400 mAh/cm³ ormor. Therefore, they respectively have a large capacity compared withthat of the electrode 8 using graphitized MCMB.

[0182] (Embodiment 3-1)

[0183] (1) A positive-electrode mixture slurry was obtained by mixing100 parts by weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL;product No. M063), 10 parts by weight of acetylene black, and 5 parts byweight of polyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of an aluminum foil having a thickness of 20 mmserving as a current collector, and drying and pressing the foil. FIG. 6is an illustration of the electrode. In the case of this embodiment, thecoating area (W1×W2) of the electrode 101 was 268×178 mm² and slurry wasapplied to both sides of the current collector 102 of 20 mm thickness ata thickness of 128 mm. As a result, the electrode thickness t was 276mm. One of the edge portions of the shorter side of the currentcollector 102 was not coated in 1 cm width and a tab 103 (aluminum witha thickness of 0.1 mm and a width of 6 mm) was welded.

[0184] (2) A negative electrode same as the above negative electrode 1except for the coating thickness of an electrode was used. Because theshape of the negative electrode is the same as the above positiveelectrode, the negative electrode is described by referring to FIG. 6.In the case of this embodiment, the coating area (W1×W2) of theelectrode 101 was 270×180 mm² and slurry was applied to both sides ofthe current collector 102 of 14 mm thickness at a thickness of 72 mm. Asa result, the electrode thickness t was 158 mm. One of the edge portionsof the shorter side of the current collector 102 was not coated in 1 cmwidth and a tab 103 (nickel with a thickness of 0.1 mm and a width of 6mm) was welded.

[0185] Only one side was coated in accordance with the same method and asingle-sided electrode of 86 mm thickness was formed formed by the samemethod except for the single-sided coating. The single-sided electrodewas positioned at the outermost in the electrode-stacked body in Item(3) (101 c in FIG. 2).

[0186] (3) An electrode-stacked body was formed by alternately stacking10 positive electrodes and 11 negative electrodes (including twosingle-sided electrodes) obtained in the above Item (1) with a separator104 (made by TONEN TAPIRUSU Co., Ltd.; made of porous polyethylene) heldbetween each of the layers as shown in FIG. 2.

[0187] (4) A bottom case 2 (refer to FIG. 1) of a battery was formed bybending a thin plate made of SUS304 having a thickness of 0.5 mm andhaving the shape shown in FIG. 4 inward along the broken lines L1 andmoreover bending it outward along the alternate long and short dashlines L2, and then arc-welding the corners A. The upper case 1 of thebattery was also formed of a thin plate made of SUS304 having athickness of 0.5 mm. Furthermore, positive electrode and negativeelectrode 3 and 4 made of SUS304 (diameter of 6 mm) and a safety-venthole (diameter of 8 mm) were formed on the upper case 1 and the positiveand negative electrodes 3 and 4 were insulated from the upper case 1 bya polypropylene packing.

[0188] (5) Each positiv-electrode tab 103 a of the electrode-stackedbody formed in the above Item (3) was welded to the positive-el ctrodetab 3 and each negative-electrode tab 103 b of it was welded to thenegatlve-eletrode tab 4 through a connection line and theelectrode-stacked body was set to the bottom case 2 and fixed by aninsulating tape to laser-weld the entire circumference along the edge Ain FIG. 1. Thereafter, a solution made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1 was pouredthrough a safety-vent hole as electrolyte and the hole was closed byusing an aluminum foil having a thickness of 0.1 mm.

[0189] (6) The formed battery has a size of 300 mm×210 mm×6 mm. Thebattery was charged by a constant-current/constant-voltage charging for18 hours, in which the battery was charged up to 4.3 V by a current of 3A and then charged by a constant voltage of 4.3 V. Then, the battery wasdischarged to 2.0 V by a constant current of 3 A. The discharge capacitywas 27.6 Ah, the energy capacity was 99 Wh, and the volume energydensity was 263 Wh/l.

[0190] (7) As a result of charging the battery and discharging thebattery at a current of 30A in a thermostatic chamber at 20 degreeCelsius by the method described in the above Item (6), rise of thebattery temperature at the end of discharge was small compared with thecase of assembled prismatic battery (thickness of 12 mm or more) havingthe same capacity.

[0191] (Embodiment 3-2)

[0192] A positive electrode was formed which was the same as that of theembodiment 3-1 except that slurry was applied to both sides of a currentcollector 102 at a thickness of 130 mm and the electrode thickness t was280 mm.

[0193] Then, a negative electrode was used which was the same as theabove negative 4 except for the coating thickness of the electrode. Thecoating area (W1×W2) of an electrode 101 is 270×180 mm² and slurry isapplied to both sides of the current collector 102 of 14 mm at athickness of 70 mm. As a result, the electrode thickness t is 154 mm. Tslurry was applied to only one side by the same method and asingle-sided electrode having a thickness of 84 mm was formed inaccordance with the same method except for the single-sided applicationof the slurry. Other points were the same as those of the embodiment3-1.

[0194] As a result of forming a battery by the same method as the caseof the embodiment 3-1 and measuring the capacity, the capacity was 28.2Ah. T the energy capacity was 102 Wh and the volume energy density was269 Wh/l.

[0195] Furthermore, a battery was formed under the same condition as thecase of each of the above embodiment by using the above negativeelectrodes 2, 3, and 5 to 7 except for the negative electrodes 1 and 4and the result same as the above was obtained.

COMPARATIVE EXAMPLE 3-1 For Comparison With Embodiments 3-1 and 3-2

[0196] A positive electrode was formed which was the same as that of theembodiment 3-1 except that slurry was applied to both sides of a currentcollector 102 and the electrode thickness t was 260 mm.

[0197] Then, a negative electrode was used which was same as the abovenegative electrode 8 except for the coating thickn ss of the electrode.In the case of this comparative example, the coating area (W1×W2) of anel strode 101 was 270×180 mm² and slurry was applied to both sides ofthe current collector 102 of 14 mm thickness at a thickness of 80 mm. Asa result, the electrode thickness t was 174 mm. A slurry was applied toonly one side by the same method and a single-sided electrode of 94 mmwas formed in accordance with the same method except for thesingle-sided application of the slurry. Other points were the same asthe case of the embodiment 3-1.

[0198] As a result of forming a battery in accordance with the samemethod as the case of the embodiment 3-1 and measuring the capacity, thecapacity was 25.8 Ah. The energy capacity was 93 Wh and the volumeenergy density was 249 Wh/l which were lower than the case of theembodiment 3-1.

[0199] [C-Type Negative Electrode]

[0200] (Formation of Electrode)

[0201] Fifty grams of artificial graphite (“KS-44” made by RONZA Co.,Ltd., central particle diameter D50=20.1 mm, particle size distributionof 0.1 to 150 mm, d002=0.336 nm, Lc.=110 nm, La=105 nm, specific surfacearea=8.2 m²/g, R value=0.23, true specific gravity of 2.25 g/cm³) and 5g of coal tar pitch from which primary QI was previously removed andwhich had a softening point of 80 degree Celsius (quinoline-insolublecomponent=trace, toluene-insoluble component=30%), and 50 g of tarmiddle oil were poured in a 500 ml separable flask and distilled at 200degree Celsius and 10 Torr. After recovering tar middle oil,distillation was stopped to obtain pitch-coating graphite.

[0202] Because the measured value of the quinoline-soluble component ofthe obtained pitch coating graphite was 6.8%, the coating ratio ofcoat-forming carbon (volatile-component contained carbon) was equal to0.068. A coating layer was carbonized by mixing 100 parts by weight ofartificial graphite (“KS-44” made by RONZA Co., Ltd.; the property wasthe same as the above mentioned) with 100 parts by weight of the pitchcoating graphite and heat-treating the mixture in a nitrogen atmosphereat 1,200 degree Celsius for 1 hour (temperature rise rate of 50 degreeCelsius/hour). The specific surface area of the obtained coatinggraphite particles was 2.5 m²/g and the average particle diameter was20.3 mm. An electrode was formed by using the coating-graphite particlesas a negative-electrode active material, acetylene black (“DENKA BLACK”made by DENKI KAGAKU KOGYO K.K.) as a conductive material, and asolution obtained by dissolving polyvinylidene fluoride (“KF#1101” madeby Kureha Chemical Industry Co., Ltd.) in N-methylpyrrolidone as abinder.

[0203] In this case, the blending ratio was set to the following ratio;coating-graphite particles: acetylene black: polyvinylidene fluoride=87:310 (weight ratio).

[0204] Three types of negative electrodes 1′ to 3′ respectively having athickness of 100 mm were formed by applying the above solution to copperfoil of 14 mm thickness with various thickness and then, drying it at 80degree Celsius for 15 min, and continuously pressing it with a rollerpress having a radius of curvature of 0.30 cm.

[0205] A capacity test was performed in accordance with the above methodby using the above negative electrodes. As an electrolyte, a solutionwas used which was obtained by dissolving LiPF₆ having a conc ntrationof 1 mol/kg in a mixed solvent consisting of a ratio of ethylenecarbonate dimethyl carbonate: methyl ethyl carbonate=7:6:6 (weightratio). Table 3 shows obtained electrode densities, initial capacities,and initial efficiencies.

[0206] A negative electrode 4′ was formed similarly to the case of thenegative electrode 1′ except for using graphitized MCMB (made by OSAKAGAS CHEMICAL; product No. 6-28). Table 3 shows obtained electrodedensities, initial capacities, and initial efficiencies. TABLE 3Electrode Negative density Initial capacity Initial efficiency electrodeNo. (g/cm³) (mAh/cm³) (%) Negative electrode 1′ 1.35 411 91 Negativeelectrode 2′ 1.46 441 91 Negative electrode 3′ 1.54 471 90 Negativeelectrode 4′ 1.44 365 89

[0207] As shown in Table 3, the negative electrodes 1′ to 3′ haveelectrode densities of 1.35 to 1.60 g/cm³, and each of them has acapacity of 400 mAh/cm³ or more, and has large capacity compared withthe capacity of the negative electrode 4′ using graphitized MCMB.

[0208] (Embodiment 4-1)

[0209] (1) A positive-electrode mixture slurry was obtained by mixing100 parts by weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL;product No. M063), 10 parts by weight of acetylene black, and 5 parts byweight of polyvinylidene fluoride (PVDF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of an aluminum foil having a thickness of 20 mmserving as a current collector, and drying and pressing the foil. FIG. 6is an illustration of an electrode. In the case of this embodiment, thecoating area (W1×W2) of the electrode 101 was 268×178 mm² and slurry wasapplied to both sides of the current collector 102 of 20 mm thickness ata thickness of 128 mm. As a result, the electrode thickness t was 276mm. One of the edge portions of the shorter side of the currentcollector 102 was not coated in 1 cm width and a tab 103 (aluminum witha thickness of 0.1 mm and a width of 6 mm) was welded.

[0210] (2) A negative electrode was used which was the same as the abovenegative electrode 2′ except for the coating thickness of an electrode.Because the shape of the negative electrode is the same as the abovepositive electrode, the negative electrode was described by referring toFIG. 6. In the case of this embodiment, the coating area (W1×W2) of theelectrode 101 was 270×180 mm² and slurry was applied to both sides ofthe current collector 102 of 14 mm thickness at a thickness of 72 mm. Asa result, the electrode thickness t was 158 mm. One of the edge portionsof the shorter side of the current collector 102 was not coated in 1 cmwidth and a tab 103 (nickel with a thickness of 0.1 mm and a width of 6mm) was welded.

[0211] Slurry was applied to only one side by the same method and asingle-sided electrode having a thickness of 86 mm was formed by thesame method except for the single-side application of the slurry. Thesingle-sided electrode was set to the outermost of the stackedelectrodes in Item (3) (101 c in FIG. 2).

[0212] (3) An electrode-stacked body was formed by alternately stacking10 positive electrodes and 11 negative electrodes (including twosingle-sided electrodes) obtained in the above Item (1) with a separator104 (made by TONEN TAPIRUSU Co., Ltd.; made of porous ethylene) heldbetween each of the electrode as shown in FIG. 2.

[0213] (4) A bottom case 2 (refer to FIG. 1) of a battery was formed bybending a thin plate made of SUS304 having a thickness of 0.5 mm andhaving the shape shown in FIG. 4, inward along the broken lines L1 andmoreover bending it outward along the alternate long and short dashlines L2, and then arc-welding the corners A. The upper case 1 of thebattery was also formed of a thin plate made of SUS304 having athickness of 0.5 mm. Furthermore, positive electrode and negativeelectrode 3 and 4 (diameter of 6 mm) and a safety-vent hole (diameter of8 mm) were formed on the upper case 1 but the positive and negativeelectrodes 3 and 4 were insulated from the upper case 1 by apolypropylene packing.

[0214] (5) Each positive-electrode tab 103 a of the electrode-stackedbody formed in the above Item (3) was welded to the positive-electrodetab 3 and each negative-electrode tab 103 b of it was welded to thenegative-eletrode tab 4 through a connection line and theelectrode-stacked body was set to the bottom case 2 and fixed by aninsulating tape to laser-weld the entire circumference along the edge Ain FIG. 1. Thereafter, a solution was made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1, and thesolution was poured through a safety-vent hole as electrolyte. The holewas closed by using aluminum foil having a thickness of 0.1 mm.

[0215] (6) The formed battery had a size of 300 mm×210 mm×6 mm. Thebattery was charged by a constant-current/constant-voltage charging for18 hours, in which the battery was charged up to 4.3 V by a current of 3A and then charged by a constant voltage of 4.3 V. Then, the battery wasdischarged to 2.0 V by a constant current of 3 A. The discharge capacitywas 27.6 Ah, energy capacity was 99 Wh, and volume energy density was263 Wh/l.

[0216] (7) As a result of charging the battery and discharging thebattery at a current of 30A in a thermostatic chamber at 20 degreeCelsius by the method described in the above Item (6), rise of thebattery temperature at the end of discharge was small compared with thecase of the assembled prismatic battery (thickness of 12 mm or more)having the same capacity.

[0217] A battery was formed under the same conditions as the case of theembodiment 4-1 by using negative electrodes same as the above negativeelectrodes 1′ and 3′ except for the coating thickness of an electrode,and the same result as the above was obtained.

COMPARATIVE EXAMPLE 4-1 For comparison With Embodiment 4-1

[0218] A positive electrode was formed which was the same as that of theembodiment 4-1 except that slurry was applied to both sides of a currentcollector 102 and the electrode thickness t was 260 mm.

[0219] Then, a negative electrode same as the above negative electrode4′ exc pt for the coating thickness of the electrode was used. In thecase of this comparative example, the coating area (W1×W2) of anelectrode 101 was 270×180 nn² and slurry was applied to both sides ofthe current collector 102 of 14 mm thickness at a thickness of 80 mm. Asa result, the electrode thickness t was 174 mm. A slurry was applied toonly one side by the same method and a single-sided electrode of 94 mmwas formed in accordance with the same method except for the single-sideapplication of the slurry. Other points were the same as the case of theembodiment 4-1.

[0220] As a result of forming a battery in accordance with the samemethod as the case of the embodiment 4-1 and measuring the capacity, thecapacity was 25.6 Ah. The energy capacity was 91 Wh and the volumeenergy density was 240 Wh/l which were lower than the case of theembodiment 4-1.

[0221] Now, descriptions of embodiments of A, B, and C-type negativeelectrodes are completed.

[0222] [Preferable Separator Used for Non-Aqueous Secondary Battery ofthe Present Invention]

[0223] In the case of the present invention, it was also allowed thatthe positive electrode 101 a and negative electrode 101 b (or negativeelectrode 101 c positioned at both outer sides in the stackedelectrodes) were alternately stacked with the separator 104 held betweeneach of the layers as shown in FIG. 2.

[0224] It is preferable to use A- or B-type separator described below indetail although the use is not limited thereby.

[0225] Forming a non-aqueous secondary battery using the above separatorinto a flat shape is advantageous for heat radiation because theradiation area increases. The thickness of the secondary battery ispreferably less than 12 mm, more preferably less than 10 mm, or stillmore preferably less than 8 mm. The lower limit of the thickness of 2 mmor more is practical when considering a packing rate of an electrode anda battery size (to obtain the same capacity, the area increases as thethickness decreases). When the thickness of the battery becomes 12 mm ormore, it is difficult to sufficiently radiate the heat in the battery tothe outside or the temperature difference between the inner portion ofthe battery and the vicinity of the surface of the battery increases andfluctuations of charge quantity and voltage in the battery increasebecause the internal resistance differs. Though a specific thickness isproperly determined in accordance with a battery capacity or energydensity, it is preferable to design a battery at a maximum thickness atwhich an expected heat radiation characteristic is obtained.

[0226] [A-Type Separator]

[0227] An A-type separator 104 is described below in detail. FIG. 7 isan illustration showing results of measuring the thickness of theseparator 104 while pressing the separator 104 in the thicknessdirection of the separator 104. In FIG. 7, X denotes a tangent of thethickness-pressure curve of the separator at the pressure F, and Ydenotes a thickness-pressure curve of the separator.

[0228] First, the condition required for the separator 104 is asfollows: when pressing the separator 104 at a pressure of 2.500 kg/cm²,the thickness A of the separator 104 is in a range not less than 0.0.02mm and not more than 0.15 mm or preferably in a range not less than 0.02mm and not more than 0.10 mm. Such a case in which the thickness A underpressure exceeds 0.15 mm is not preferable because the thickness of theseparator 104 is too large, the internal resistance increases or theratio of the separator 104 occupying the inside of the batteryincreases, and a sufficient capacity cannot be obtained. However, such acase in which the thickness A under pressure is less than 0.02 mm is notpractically preferable because it is difficult to manufacture theseparator.

[0229] As shown in FIG. 7, the separator 104 is resilient. Therefore,when applying a load to the separator 104 in its thickness direction (inFIG. 7, the abscissa shows pressure applied to the separator), thethickness of the separator 104 quickly decreases at the initial time.However, when further increasing the load, the change of the thicknessof the separator 104 slowly decreases and then, the thickness hardlychanges even if further applying the load. In this case, it is animportant point that a separator assembled into a battery hasresiliency. It is also important that the pressure applied to theseparator is low in the case of a non-aqueous secondary battery althoughthe pressure changes depending on the battery size, wall thickness orwall material of the case, or other design factors, and that theseparator has resiliency at such a low pressure. Therefore, inpreferable separator, when the absolute value of the change rate of thethickness of the separator 104 to a pressure (kg/cm²). (in FIG. 7, theabsolute value of the tilt of the tangent line of the thickness-pressurecurve Y of a separator at the pressure F, e.g. the absolute value of thetilt of the tangent line X) is defined as B (mm/(kg/cm²)), the pressureF which renders B/A=1 is in a range not less than 0.050 kg/cm² and notmore than 1.000 kg/cm² or more preferably in a range not less than 0.050kg/cm² and not more than 0.700 kg/cm². A case in which the pressure F islower than 0.050 kg/cm² is not preferable because a separator alreadyloses resiliency and a sufficient cycle characteristic is not obtained.A case in which the pressure F exceeds 1.000 kg/cm² is not preferablebecause a separator frequently has a very high resiliency and therefore,it is difficult to build the separator in a battery.

[0230] The porosity of the separator 104 is 40% or more, preferably 50%or more under the pressure of 2.500 kg/cm², that is, when the separatorhas the above thickness A mm. A case in which the porosity is less than40% is not preferable because an electrolyte cannot be sufficientlyheld, the internal resistance increases, or a sufficient cyclecharacteristic is not obtained.

[0231] It is preferable to use non-woven fabric as a separator meetingthe above conditions. In this case, the separator can be easilymanufactured. Because non-woven fabric for a battery is finally finishedby using a technique such as thermal pressing in order to adjust thethickness. Non-woven fabric has been frequently lost resiliency in theabove thickness-adjusting step (some of non-woven fabrics used forclothing do not include the thickness-adjusting step and most non-wovenfabrics are resilient). However, a separator used for a non-aqueoussecondary battery of the present invention can be easily manufactured byproperly setting a condition such as the thermal pressing.

[0232] Though a material of the separator 104 is not limited, it ispossible to use polyolefin such as polyethylene or polypropylene,polyamide, kraft paper, glass, etc. However, polyethylene orpolypropylene is preferable from the viewpoints of cost and moisture.Furthermore, when using polyethylene or polypropylene for the separator104, the unit weight of the separator is preferably not less than 5 g/m²and not more than 30 g/m², more preferably not less than 5 g/m² and notmore than 20 g/m², or still more preferably not less than 8 g/m² and notmore than 20 g/m². A case in which the unit weight of a separatorexceeds 30 g/m² is not preferable because the separator becomes toothick or the porosity lowers and the internal resistance of a batteryincreases. A case in which the unit weight is less than 5 g/m² is notpreferable because a practical strength cannot be obtained.

[0233] The A-type separator is more minutely described below by using anembodiment of the separator.

[0234] (Embodiment 5-1)

[0235] (1) A positive-electrode mixture slurry was obtained by mixing100 parts by weight of LiCo₂O₄, 8 parts by weight of acetylene black,and 3 parts by weight of polyvinylidene fluoride (PVdF) with 100 partsby weight of N-methylpyrrolidone (NMP). A positive electrode wasobtained by applying the slurry to both sides of aluminum foil having athickness of 20 mm serving as a current collector, and drying andpressing the foil. FIG. 6 is an illustration of an electrode. In thecase of this embodiment, the coating area (W1×W2) of the electrode 101is 268×178 mm² and slurry was applied to both sides of the currentcollector 102 of 20 mm thickness at a thickness of 105 mm. As a result,the electrode thickness t is 230 mm. One of the edge portions of theshorter side of the current collector 102 was not coated in 1 cm widthand a tab 103 (aluminum with a thickness of 0.1 mm and a width of 6 mm)was welded.

[0236] (2) A negative-electrode mixture slurry was obtained by mixing100 parts by weight of graphitized mesocarbon microbeads (MCMB, made byOSAKA GAS CHEMICAL Co., Ltd., product No. 6-28) and 10 parts by weightof PVdF with 90 parts by weight of NMP. A negative electrode wasobtained by applying the slurry to both sides of copper foil having athickness of 14 mm serving as a current collector, drying the foil andthen pressing the foil. Because the shape of the electrode is the sameas that of the above-described positive electrode, the negativeelectrode is described below by referring to FIG. 6. In the case of thisembodiment, the coating area (W1×W2) of the electrode 101 was 270×180mm² and the slurry was applied to both sides-of the current collector102 of 14 mm thickness at a thickness of 110 mm. As a result, theelectrode thickness t was 234 mm. One of the edge portions of theshorter side of the current collector 102 was not coated in 1 cm widthand a tab 103 (nickel with a thickness of 0.1 mm and a width of 6 mm)was welded.

[0237] Slurry was applied to only one side in accordance with the samemethod and a single-sided electrode having a thickness of 124 mm was inaccordance with the same method formed except for th single-sideapplication of the slurry. The single-sided electrode was set to theoutermost of the stack d electrod s in Item (3) (101 c in FIG. 2).

[0238] (3) An electrode-stacked body was formed by alternately stacking8 positive electrodes and 9 negative electrodes (including twosingle-sided electrodes) obtained in the above Item (1) with a separator104 (polyethylene-polypropylene non-woven fabric) held between each ofthe electrodes. Table 4 shows characteristics of the separator.

[0239] A pressure F was calculated by stacking five separatorsrespectively cut into 5×5 cm² and measuring a pressure-thickness curveinitially every 0.005 kg/cm² and then every 0.025 kg/cm² in a range from0.025 kg/cm² up to 0.500 kg/cm² and then every 0.100 kg/cm² in a rangefrom 0.500 kg/cm² up to 2.50 kg/cm² in accordance with the methoddescribed by referring to FIG. 7. Though measurement was repeated threetimes every 5 hours, the value of F and the thickness A under pressureof 2.500 kg/cm² were hardly changed.

[0240] (4) The bottom case 2 of the battery (refer to FIG. 1) was formedby wringing a 0.5 mm thin plate made of SUS304 into a depth of 5 mm. Theupper case 1 of the battery was also formed of a 0.5 mm thin plate madeof SUS304. The positive and negative electrodes made of SUS304 3 and 4(diameter of 6 mm) were set to the upper case and a safety-vent hole(diameter of 8 mm) was formed on the upper case and the positive andnegative electrodes 3 and 4 were insulated from the upper case 1 by apolypropylene packing.

[0241] (5) Each positive-electrode tab 103 a of the electrode-stackedbody formed in the above Item (3) was welded to the positive-electrodetab 3 and each negative-electrode tab 103 b of it was welded to thenegative-eletrode tab 4 through a connection line and theelectrode-stacked body was set to the bottom case 2 and fixed by aninsulating tape to laser-weld the entire circumference of the corner Ain FIG. 1. Thereafter, a solution made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1 was pouredthrough a safety-vent hole as an electrolyte and the hole was closed byusing aluminum foil having a thickness of 0.1 mm.

[0242] (6) The obtained battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a constant current of 10 A. The discharge capacity was 23.3 Ah. Thetemperature rise of the battery while discharged was small compared withthe case of a prismatic battery (battery having a thickness of 12 mm ormore) having the same capacity.

[0243] (7) The capacity when repeating charge and discharge by 10 cyclesby using the battery under the same condition as the above mentioned was21.5 Ah.

[0244] (Embodiment 5-2)

[0245] A battery was formed similarly to the case of the embodiment 5-1except for using the polypropylene non-woven fabric of the embodiment5-2 shown in Table 4 as a separator. The battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a constant current of 10 A. The discharge capacity was 22.8 Ah. Thecapacity when repeating charge and discharge by 10 cycles under the samecondition as the case of the embodiment 5-1 by using the battery was20.9 Ah.

COMPARATIVE EXAMPLE 5-1 For comparison With Embodiments 5-1 and 5-2

[0246] A battery was formed similarly to the case of the embodiment 5-1except for using the polyethylene micro-porous film of the comparativeexample 5-1 shown in Table 4 as a separator and change the number oflayered electrodes to 10 positive electrodes and 11 negative electrodes(including two single-sided electrodes). The battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a current of 10 A. The discharge capacity was 25.2 Ah. The capacitywhen repeating charge and discharge by 10 cycles under the samecondition as the case of the embodiment 5-1 by using the battery was19.0 Ah.

[0247] The separator is used for, for example, an 18650-type cylindricalbattery. In the case of the cylindrical battery, cycle deterioration at10 initial cycles is 90% or more. However, when using a flat battery,the discharge capacity was lowered up to the 10th cycle though theinitial capacity was high because a separator was thin and the number oflayered electrodes was large compared with Embodiments 5-1 and 5-2.

COMPARATIVE EXAMPLE 5-2

[0248] A battery was formed similarly to the case of the embodiment 5-1except for using the polypropylene non-woven fabric (pressure F exceeds0.025 kg/cm² but it is lower than 0.050 kg/cm²) of the comparativeexample 5-2 shown in Table 4 as a separator. The battery was charged bya constant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a constant current of 10 A. The discharge capacity was 21.0 Ah. Thecapacity when repeating charge and discharge by 10 cycles under the samecondition as the case of the embodiment 5-1 by using the battery was17.0 Ah.

[0249] Though the separator was the same as the separator of theembodiment 5-1 in porosity and thickness, it was not resilient.Therefore, when using the separator for a flat battery, the dischargecapacity was lowered up to the 10th cycle.

COMPARATIVE EXAMPLE 5-3

[0250] A battery was formed similarly to the case of the embodiment 5-1except for using the glass non-woven fabric of the comparative example5-3 shown in Table 4 as a separator and change the number of layeredelectrodes to 6 positive electrodes and 7 negative electrodes (includingtwo single-sided electrodes). The battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charg d up to 4.1 V by a current of 4 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharg d up to 2.5V by a current of 8 A. The discharge capacity was 18.1 Ah. The capacitywhen repeating charge and discharge by 10 cycles under the samecondition as the case of the embodiment 5-1 by using the battery was17.3 Ah.

[0251] The separator is sufficiently resilient and has a capacityretension rate equal to those of the embodiments 5-1 and 5-2 after 10cycles pass. However, because the separator has a large thickness, thecapacity was lower than those of the embodiments 5-1 and 5-2. TABLE 4Porosity at Unit Thickness A Pressure F 2.5 kg/cm² weight Material (mm)(kg/cm²) (%) (g/m²) Embodiment Polyethylene-polypropylene 0.087   0.50089.1 13.7 5-1 non-woven fabric Embodiment Polypropylene non-woven 0.072  0.050- 83.0 13.1 5-2 fabric 0.075 Comparative Polyethylenemicro-porous 0.025 <0.025 41.0 15.5 example 5-1 film ComparativePolypropylene non-woven 0.100   0.025 < 73.0 32 example 5-2 fabric<0.050 Comparative Glass non-woven fabric 0.232 0.200 >90 — example 5-3

[0252] [B-Type Separator]

[0253] A B-type separator is described below in detail. FIG. 8 shows aside view and a perspective view of a separator used for the non-aqueoussecondary battery shown in FIG. 1. As shown in FIG. 8, the separatorcomprises a first separator 104 a and two second separators 104 b, inwhich the second separators 104 b were arranged at both sides of thefirst separator 104 a. The configuration of the separator is notlimited. Two or more different types of separators can be used as longas the separators meet the following conditions. For example, on firstseparator 104 a and one second separator 104 b arranged as shown in FIG.9 may be used, or separators of different types may be used instead ofsecond separators 104 b of the same type shown in FIG. 8, or a secondseparator may be placed between two first separators in contrary to whatis shown in FIG. 8.

[0254] Then, a first separator is more minutely described below. FIG. 7is an illustration showing results of measuring the thickness of thefirst separator while applying a pressure to the first separator in itsthickness direction. In FIG. 7, X denotes a tangent of the thicknesscurve of the separator to pressure at a pressure F and Y denotes athickness curve of the separator to pressure.

[0255] First, when pressing the first separator at a pressure of 2.500kg/cm² as a condition required for the first separator, the thickness Aof the first separator is kept in a range not less than 0.02 mm and notmore than 0.15 mm, or preferably kept in a range not less than 0.02 mmand not more than 0.10 mm. A case in which the thickness under pressureexceeds 0.15 mm is not preferable because the thickness of the separatoris too large, the internal resistance increases or the rate for theseparator to occupy the inside of a battery increases, and a sufficientcapacity is not obtained. However, a case in which the thickness A underpressure is less than 0.02 mm is not preferable for practical usebecause it is difficult to manufacture the battery.

[0256] As shown in FIG. 7, the first separator is resilient and whenapplying a load to the first separator in its thickness direction (inFIG. 7, abscissa shows pressure applied to separator), the thickness ofthe first separator quickly decr ases at the initial point of time. Howver, when further increasing a load, change of the thickness of thefirst separator slowly decreases and then, thickness is hardly changed.In this case, it is important that a separator is resilient when abattery is formed. In the case of a flat non-aqueous secondary battery,the battery size, or wall thickness or wall material of a case arechanged depending on other design elements. However, it is importantthat a pressure to be applied to a separator is low and the separator isresilient at a low pressure. Therefore, in a preferable separator, whenassuming the absolute value of the change rate of the thickness (mm) ofthe first separator to a pressure (kg/cm²) (in FIG. 7, tangent ofthickness curve Y of separator to pressure at pressure F, such asabsolute value of tilt of tangent X) as B (mm/(kg/cm²)), the pressure Fin which B/A is equal to 1 is not less than 0.050 kg/cm² and not morethan 1.000 g/cm² or more preferably not less than 0.050 kg/cm² and notmore than 0.700 kg/cm². A case in which the pressure F is lower than0.050 kg/cm² is not preferable because a separator already loses itsresiliency when a battery is formed and a sufficient cyclecharacteristic is not obtained or a case in which the pressure F exceeds1.000 kg/cm² is not preferable because a separator frequently has a verylarge resiliency and it is difficult to set the separator in a battery.

[0257] When the porosity of the first separator at a pressure of 2.500kg/cm², that is, at the above thickness of A mm is kept at 40% or moreor preferably kept at 50% or more. A case in which the porosity is lessthan 40% is not preferable because an electrolyte cannot be sufficientlykept, the internal pressure rises, or a sufficient cycle characteristiccannot be obtained.

[0258] It is preferable to use non-woven fabric for the first separatormeeting the above conditions. In this case, it is easy to manufacturethe separator. In general, non-woven fabric for a battery is finallyfinished in order to adjust the thickness by a technique such as thermalpressing. Non-woven fabric has frequently lost its resiliency so far inthe thickness-adjusting step (some of non-woven fabrics for clothing donot have the thickness-adjusting step and most non-woven fabrics areresilient). However, a separator used for a non-aqueous secondarybattery of the present invention can be easily manufactured by properlysetting a condition such as the above thermal pressing.

[0259] Then, the second separator is more minutely described below. Thesecond separator is a micro-porous film having a pore diameter of 5 mmor less or preferably having a pore diameter of 2 mm or less and havinga porosity of 25% or more or preferably having a porosity of 30% ormore. A pore diameter can be observed by an electron microscope. Theabove micro-porous film can use a micro-porous film generally marketedfor a lithium ion battery. The second separator is used to compensate adisadvantage that a slight short circuit easily occurs when the batteryis manufactured or charged or discharged because the separator has acomparatively large pore diameter and a high porosity. Therefore, a casein which the pore diameter of the second separator exceeds 5 mm is notpreferable because it is impossible to compensate the abovedisadvantage. A case in which the porosity is less than 25% is notpreferable because an electrolyte cannot be sufficiently kept or theinternal resistance rises. Furthermore, because the thickness of thesecond separator is 0.05 mm or less, it is possible to use a separatorhaving a thickness of not more than 5 mm and not more than 30 mm. Thisis because it is difficult to manufacture the separator if the thicknessis too small or the internal resistance tends to rise if the thicknessis too large.

[0260] Materials of the first and second separators are not limited. Forexample, it is possible to use polyolefins such as polyethylene andpolypropylene, and polyamide, kraft paper, and glass. However,polyethylene and polypropylene are preferable from the viewpoints ofcost, and moisture.

[0261] When using polyethylene or polypropylene for the first separator,the unit weight of the first separator is preferably not less than 5g/m² and 30 g/m², more preferably not less than 5 g/m² and not more than20 μm², or still more preferably not less than 8 g/m² and not more than20 μm². A case in which the unit weight of a separator exceeds 30 g/m²is not preferable because the separator becomes too thick, the porositylowers, or the internal resistance of a battery rises. A case in whichthe unit weight is less than 5 g/m² is not preferable because a strengthfor practical use cannot be obtained.

[0262] Though various combinations of materials of the first and secondseparators can be considered, it is preferable to combine differentmaterials. In this case, the effect of shutdown of the operation of thebattery is further expected, in which the shutdown occurs when a batterycauses thermal runaway.

[0263] It is preferable to manufacture the first and second separatorsby laminating them together. To laminate them together, the followingmethod can be used: mechanical mutual laminating by pressing, mutuallaminating by thermal rollers, mutual laminating by chemicals, or mutuallaminating by adhesive. For example, to combine one separator mainlymade of polyethylene with the other separator mainly made ofpolypropylene, it is allowed to laminate them while melting the surfacelayer of the polyethylene separator by a thermal roller, takingpolyethylene powder into polypropylene non-woven fabric, or laminatingnon-woven fabrics made of a material obtained by coating the surface ofpolypropylene fiber with polyethylene together by thermal rollers. It isimportant to perform mutual laminating without crushing voids of theabove separators.

[0264] Embodiments of a B-type separator are more specifically describedbelow.

[0265] (Embodiment 6-1)

[0266] (1) A positive-electrode mixture slurry was obtained by mixing100 parts by weight of LiCo₂O₄, 8 parts by weight of acetylene black,and 3 parts by weight of polyvinylidene fluoride (PVdF) with 100 partsby weight of N-methylpyrrolidone (NMP). A positive electrode wasobtained by applying the slurry to both sides of aluminum foil having athickness of 20 mm serving as a current collector, and drying andpressing the foil. FIG. 6 is an illustration of an electrode. In thecase of this embodiment, the coating area (W1×W2) of the electrode 101is 268×178 mm² and slurry was applied to both sides of the currentcollector 102 of 20 mm thickness at a thickness of 95 mm. As a result,the electrode thickness t was 210 mm. One of the edge portions of theshorter side of the current collector 102 was not coated in 1 cm widthand a tab 103 (aluminum with a thickness of 0.1 mm and a width of 6 mm)was welded.

[0267] (2.) A negative-electrode mixture slurry was obtained by mixing100 parts by weight of graphitized mesocarbon microbeads (MCMB, made byOSAKA GAS CHEMICAL Co., Ltd., product No. 6-28) and 10 parts by weightof PVdF with 90 parts by weight of NMP. A negative electrode wasobtained by applying the slurry to both sides of copper foil having athickness of 14 mm serving as a current collector, drying the foil andthen pressing the foil. Because the shape of the electrode is the sameas that of the above-described positive electrode, the negativeelectrode is described below by referring to FIG. 6. In the case of thisembodiment, the coating area (W1×W2) of the electrode 101 was 270×180mm² and the slurry was applied to both sides of the current collector102 of 14 mm thickness at a thickness of 105 mm. As a result, theelectrode thickness t was 224 mm. One of the edge portions of theshorter side of the current collector 102 was not coated in 1 cm widthand a tab 103 (nickel with a thickness of 0.1 mm and a width of 6 mm)was welded.

[0268] Slurry was applied to only one side in accordance with the samemethod and a single-sided electrode having a thickness of 119 mm wasformed in accordance with the same method except for the single-sidedapplication of the slurry. The single-sided electrode is set to theoutermost of the electrode-stacked body in Item (3) (101 c in FIG. 2).

[0269] (3) In the case of this embodiment, as shown in Table 5, anelectrode-stacked body was formed by using polyethylene-polypropylenenon-woven fabric as a first separator and a polyethylene micro-porousfilm as a second separator so that the positive-electrode side became amicro-porous film, stacking the first and second separators similarly tothe case of the separators shown in FIG. 9, and alternately stacking 8positive electrodes and 9 negative electrodes (including twosingle-sided electrodes) obtained in the above Item (1) through aseparator 104 (constituted by stacking a polyethylene-polypropylenenon-woven fabric and a polypropylene micro-porous film). Table 5 showscharacteristics of the separators.

[0270] A pressure F was calculated in accordance with the methoddescribed for FIG. 7 by stacking five separators respectively cut into5×5 cm² and measuring the pressure-thickness curve of the firstseparator at first every 0.005 kg/cm² ₁ and then every 0.025 kg/cm² inthe pressure range from 0.025 kg/cm² up to 0.500 kg/cm² and every 0.100kg/cm² in the pressure range from 0.500 kg/cm² up to 2.500 kg/cm². As aresult of repeating the above measurement three times every 5 hours, thevalue of F and the thickness A at a pressure of 2.500 kg/cm² were hardlychanged.

[0271] (4) The bottom case 2 of the battery (refer to FIG. 1) was formedby deep drawing of a 0.5 mm thin plate made of SUS304 into a depth of 5mm. The upper case 1 of the battery was also formed of a 0.5 mm thinplate made of SUS304. The positive and negative electrodes made ofSUS304 3 and 4 (diameter of 6 mm) were set to the upper case and asafety-vent hole (diameter of 8 mm) was formed on the upp r case but thepositive and negative electrodes 3 and 4 were insulated from the uppercase 1 by a polypropylene packing.

[0272] (5) Each positive-electrode tab 103 a of the electrode-stackedbody formed in the above Item (3) was welded to the positive-electrodetab 3 and each negative-electrode tab 103 b of it was welded to thenegative-eletrode tab 4 through a connection line and theelectrode-stacked body was set to the bottom case 2 and fixed by aninsulating tape to laser-weld the entire circumference of the corner Ain FIG. 1. Thereafter, a solution made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1 was pouredthrough a safety-vent hole as an electrolyte and the upper case wasclosed by using aluminum foil having a thickness of 0.1 mm. The total offive batteries were formed as described above.

[0273] (6) The obtained battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the batteries were discharged up to2.5 V by a constant current of 10 A. Discharge capacities of the fivebatteries ranged between 21.1 and 21.4 Ah. The temperature rise of thebatteries while discharged was small compared with the case of aprismatic battery (battery having a thickness of 12 mm or more) havingthe same capacity.

[0274] (7) Capacities when repeating charge and discharge by 10 cyclesunder the same condition as the above by using the above five batteriesranged between 19.2 and 20.1 Ah.

[0275] (Embodiment 6-2)

[0276] A battery was formed similarly to the case of the embodiment 6-1except for using the polypropylene non-woven fabric of the embodiment6-2 shown in Table 5 as a first separator. The battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the battery was discharged up to 2.5V by a constant current of 10 A. The discharge capacity was 21.0 Ah. Thecapacity when repeating charge and discharge by 10 cycles under the samecondition as the case of the embodiment 6-1 by using the battery was19.0 Ah.

COMPARATIVE EXAMPLE 6-1 For Comparison With Embodiment 6-1

[0277] Five batteries were formed similarly to the case of theembodiment 6-1 except for using only the polyethylene-polypropylenenon-woven fabric same as the first separator of the embodiment 6-1 shownin Table 5 as a first separator without using a second separator andchange the number of stacked electrodes to 8 positive electrodes(thickness of either-side electrode layer was 105 mm) and 9 negativeelectrodes (including two single-sided electrodes and thickness ofeither-side electrode layer was 110 mm). The battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then, the batteries were discharged up to2.5 V by a constant current of 10 A. The discharge capacities of thr ebatteries ranged between 23.1 and 23.3 Ah but the capacities of tworemaining batteries were 19.5 Ah and 14.3 Ah and a slight short circuitwas found. Because the comparative example 6-1 did not use a secondseparator, the electrode packing rate was improved compared with thecase of the embodiment 6-1 but a slight short circuit easily occurredthrough the initial capacity was high. TABLE 5 Porosity at UnitThickness A Pressure F 2.5 kg/cm² weight Separator Material (mm)(kg/cm²) (%) (g/m²) Embodiment First Polyethylene- 0.087 0.500 89.1 13.76-1 separator polypropylene non- woven fabric Second Polyethylene micro-0.025 <0.025   41.0 15.5 separator porous film Embodiment FirstPolypropylene non- 0.072 0.050- 83.0 13.1 6-2 separator woven fabric0.075

[0278] [Positioning of Electrode Unit]

[0279] A preferred embodiment of the present invention for positioningan electrode unit using a separator is described below. In the case ofthis embodiment, a separator 104 is bonded to a positive electrode 101 aand/or negative electrodes 101 b and 101 c.

[0280] It has been very difficult so far to stack a positive electrode,a negative electrode, and a separator having a size of 272×182 mm largerthan the negative electrode while accurately positioning them which havedifferent size to each other. However, this embodiment makes it possibleto solve the above problem by bonding at least one of a plurality ofseparators to a positive or negative electrode or to both positive andnegative electrodes. In this case, it is more preferable to bond aplurality of separators to a positive or negative electrode or to bothpositive and negative electrodes or particularly preferable to bond allseparators to a positive or negative electrode or to both positive andnegative electrodes. This embodiment solves the above problem by bondingthe separator 104 of this embodiment to the positive electrode 101 aand/or negative electrodes 101 b and 101 c. When setting dimensions ofthe positive electrode 101 a to 268×178 mm, it is necessary to makedimensions of the negative electrodes 101 b and 101 c slightly largerthan those of the positive electrode 101 a in order to preventdeposition of lithium on a negative electrode. For example, it isnecessary to adjust dimensions of the negative electrodes 101 b and 101c to 270×180 mm.

[0281] Specifically, as shown in FIGS. 11A to 11C, a positive electrodeunit 111 a is formed by bonding a positive electrode 111 a with aseparator 104, a negative electrode unit 111 b is formed by bonding anegative electrode 101 b with the separator 104, and a single-sidednegative electrode unit 111 c is formed by bonding a single-sidednegative electrode 101 c with the separator 104. In this case, the sizeof the separator 104 is equal to each other irrelevant to the sizes ofthe positive electrode 101 a and negative electrodes 101 b and 101 c.Therefore, by aligning only the separator 104, it is possible to easilystack the positive electrode 101 a, negative electrodes 101 b and 101 chaving different sizes, and separator 104.

[0282] Because the separator 104 is not shifted when bonding it with thepositive electrode 101 a or negative electrodes 101 b and 101 c, it ispossible to make the size of the separator 104 equal to the size of thenegative electrodes 101 b and 101 c. By removing the portion of aseparator protruding beyond the electrodes, it is possible to improvethe electrode packing efficiency corresponding to the size of theremoved portion. A case is described above in which the s parator 104 isbonded to the positive electrode 101 a or negative electrodes 101 b and101 c which are previously cut into predetermined dimensions. However,bonding of a separator is not limited to the above case. For example, itis possible to bond a separator to hoop electrodes and then cut theelectrodes. Thus, it is possible to use various methods.

[0283] A method for bonding the separator 104 with the positiveelectrode 101 a and/or negative electrodes 101 b and 101 c is notlimited. However, it is important that all or most of pores of theseparator 104 are not blocked (the separator does not have electronconductivity as raw material, and thus it must hold an electrolyte andhave pores through which ions held in the electrolyte move betweenpositive and negative electrodes). Namely, it is important thatelectrolyte passages are securely maintained to hold the penetrationthrough the separator 104 from the front surface to the rear surface.

[0284] Specifically, methods for bonding the separator 104 with thepositive electrode 101 a and/or negative electrodes 101 b and 101 cinclude mechanical bonding by pressing, bonding due to fusion of a partof a separator, bonding by chemicals, and bonding by adhesive and so on.Particularly, it is preferable to fuse a separator by heat and bond itwith an electrode because impurities are not contained, the separator isnot easily creased, and moreover warpage or burr of the electrodeproduced due to a slit or the like can be corrected at the same time. Inthis case, it is possible to easily bond a separator made ofpolyethylene having a low fusing point. In the case of non-woven fabric,when using a composite separator made of materials having differentfusing points, for example, when using polypropylene as the corematerial of fiber and polyethylene as an external layer or mixingpolyethylene powder in polypropylene non-woven fabric, it is possible tomore easily bond the separator without closing pores of the separator. Amethod of mixing polyethylene into an electrode and bonding apolypropylene separator is a simple method.

[0285] When bonding a separator with an electrode by fusing theseparator, it is preferable to heat the electrode so that the verysurface of the separator is fused when the separator contacts theelectrode. In this case, it is possible to bond the separator with theelectrode by heating the electrode up to a temperature equal to thefusing point of the separator or higher and pressing them in a shorttime without closing pores of the separator. In this case, it is notnecessary that the entire surface of the electrode is bonded with theentire surface of the separator. It is allowed that a part of theelectrode is bonded with a part of the separator so that their positionis not shifted when the battery is formed.

[0286] The bonding structure of the positive electrode 101 a, negativeelectrodes 101 b and 101 c, and separator 104 is effective when stackingpluralities of electrodes and separators whose positioning isparticularly difficult, particularly when stacking five electrodes ormore and five separators or more, however it is possible to use thisstructure for other cases.

[0287] Embodiments for positioning an electrode unit using a spac r aremore specifically described below.

[0288] (Embodiment 7-1)

[0289] (1) A positive-electrode mixture slurry was obtained by mixing100 parts by weight of LiCO₂O₄, 8 parts by weight of acetylene black,and 3 parts by weight of polyvinylidene fluoride (PVdF) with 100 partsby weight of N-methylpyrrolidone (NMP). A positive electrode wasobtained by applying the slurry to both sides of aluminum foil having athickness of 20 mm serving as a current collector, and drying andpressing the foil. FIG. 6 is an illustration of an electrode. In thecase of this embodiment, the coating area (W1×W2) of the electrode 101was 268×178 mm² and slurry was applied to both sides of the currentcollector 102 of 20 mm thickness at a thickness of 95 mm. As a result,the electrode thickness t was 210 mm. One of the edge portions of theshorter side of the current collector 102 was not coated in 1 cm widthand a tab 103 (aluminum with a thickness of 0.1 mm and a width of 6 mm)was welded.

[0290] (2) (2) A negative-electrode mixture slurry was obtained bymixing 100 parts by weight of graphitized mesocarbon microbeads (MCMB,made by OSAKA GAS CHEMICAL Co., Ltd., product No. 6-28) and 10 parts byweight of PVDF with 90 parts by weight of NMP. A negative electrode wasobtained by applying the slurry to both sides of copper foil having athickness of 14 mm serving as a current collector, drying the foil andthen pressing the foil. Because the shape of the electrode is the sameas that of the above-described positive electrode, the negativeelectrode is described below by referring to FIG. 6. In the case of thisembodiment, the coating area (W1×W2) of the electrode 101 is 270×180 mm²and the slurry was applied to both sides of the current collector 102 of14 mm thickness at a thickness of 105 mm. As a result, the electrodethickness t was 224 mm. One of the edge portions of the shorter side ofthe current collector 102 was not coated in 1 cm width and a tab 103(aluminum with a thickness of 0.1 mm and a width of 6 mm) was welded.

[0291] Slurry was applied to only one side in accordance with the samemethod and a single-sided electrode having a thickness of 119 mm wasformed in accordance with the same method except for the single-sidedapplication of the slurry. The single-sided electrode was set to theoutermost of the electrode-stacked body in Item (3) (101 c in FIG. 2).

[0292] (3) A positive electrode unit 111 a, negative electrode unit 111b, and single-sided negative electrode unit 111 c were formed by bondinga separator 104 obtained by laminating polyethylene-polypropylenenon-woven fabric of 272×180 mm² (thickness of 87 mm) and a polypropylenemicro-porous film (thickness of 25 mm) to a positive electrode 101 a andnegative electrodes 101 b and 101 c at the positional relation shown inFIGS. 12A to 12C. Each electrode was bonded with thepolyethylene-polypropylene non-woven fabric side of the separator 104.Specifically, the separator 104 and electrodes (positive electrode 101 aand negative electrodes 101 b and 101 c) were stacked in the order at apredetermined position and heated from the electrode side by an iron atapproximately 140 degree Celsius to bond them. After bonding them, theseparator 104 was observed by removing it from some of the electrodeunits 111 a, 111 b, and 111 c. As a result, the state of surface poresof the separator 104 was hardly changed from the state before theseparator 104 was bonded. An electrode-stacked body was formed byalternately stacking eight positive-electrode units 111 a, sevennegative-electrode units 111 b, one single-sided negative-electrode unit111 c, one single-sided negative electrode 101 c not bonded with theseparator 104, and the separator 104 as shown in FIG. 10.

[0293] (4) The bottom case 2 of the battery (refer to FIG. 1) was formedby deep drawing of a 0.5 mm thin plate made of SUS304 into a depth of 5mm. The upper case 1 of the battery was also formed of a 0.5 mm thinplate made of SUS304. The positive and negative electrodes made ofSUS304 3 and 4 (diameter of 6 mm) were set to the upper case and asafety-vent hole (diameter of 8 mm) was formed on the upper case but thepositive and negative electrodes 3 and 4 were insulated from the uppercase 1 by a polypropylene packing.

[0294] (5) Each positive-electrode tab 103 a of the electrode-stackedbody formed in the above Item (3) was welded to the positive-electrodetab 3 and each negative-electrode tab 103 b of it was welded to thenegative-eletrode tab 4 through a connection line and theelectrode-stacked body was set to the bottom case 2 and fixed by aninsulating tape to laser-weld the entire circumference of the corner Ain FIG. 1. Thereafter, a solution was made by dissolving LiPF₆ at aconcentration of 1 mol/l in a solvent obtained by mixing ethylenecarbonate and diethyl carbonate at a weight ratio of 1:1. The solutionwas poured through a safety-vent hole as an el ctrolyte and the uppercase was closed by aluminum foil having a thickness of 0.1 mm. The totalof five batteries were formed.

[0295] (6) The obtained battery was respectively charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.1 V by a current of 5 A and then charged bya constant voltage of 4.1 V. Then the batteries were discharged up to2.5 V by a constant current of 10 A. Discharge capacities ranged between21.3 and 21.5 Ah. The temperature rise of the batteries while dischargedwas small compared with the case of a prismatic battery (battery havinga thickness of 12 mm or more) having the same capacity.

COMPARATIVE EXAMPLE 7-1

[0296] Five batteries were formed similarly to the case of theembodiment 7-1 except that a separator was not bonded. The obtainedbattery was charged by a constant-current/constant-voltage charging for8 hours, in which the battery was charged up to 4.1 V by a current of 5A and then charged by a constant voltage of 4.1 V. Then, the batterieswere discharged up to 2.5 V by a constant current of 10 A. Dischargecapacities of three batteries ranged between 20.9 and 21.3 Ah but thoseof two remaining batteries were 18.5 and 14.3 Ah and a slight shortcircuit occurred.

[0297] Now, description of positioning of A- and B-type separators andan electrode unit using a separator is completed.

[0298] A preferable control method of the above secondary batteries ofthe present invention is described below by referring to theaccompanying drawings. FIG. 13 shows a secondary battery 111 embodyingthe present invention. The battery 111 is provided with a positiveterminal 112 p and a negative terminal 112 n. These positive andnegative terminals are generally attached to a battery. Charge anddischarge of a battery have been controlled so far by measuring thevoltage, internal resistance, current between these two terminals, etc.A battery of the present invention is further provided withoperation-characteristic measuring terminals 113 p, 113 n, 114 p, and114 n for measuring internal information of the battery. For example,fluctuation of temperatures in a battery can be measured by connectingthe end of a thermocouple reaching the central portion of the battery tothe positive and negative terminals 113 p and 113 n and therebymeasuring the temperature of the inner portion of the battery, moreoverconnecting the end of a thermocouple located nearby the surface of thebattery to the positive and negative terminals 114 p and 114 n andthereby measuring the fluctuation of temperatures in the battery, andcomparing these measured values. Voltages in the battery can be measuredby connecting voltage-measuring lines extending from different portionsof the battery to the terminals 113 p, 113 n, 114 p, and 114 n andmeasuring the potential difference from the positive terminal 112 p.Furthermore, it is possible to measure the voltage fluctuation in thebattery by measuring voltages between the terminals 113 p to 113 n andbetween the terminals 114 p to 114 n. Data signals thus measured aresent to a control unit through connection lines AA1 to AAn in the blockdiagram (FIG. 14) to determine the fluctuation d gree by the controlunit, output a command for changing charge and discharge conditions orstopping charg and discharge to a charge-and-discharge control unit, oroutput a cooling-fan operating command and other operation controlcommands in accordance with the fluctuation degree. As a result, even iffluctuation of operation characteristics occurs in the battery, it ispossible to eliminate or moderate the fluctuation or prevent thedeterioration of the safety or reliability due to the fluctuation, byconducting a control in accordance with the fluctuation.

[0299] A control method of the present invention is used for a householdenergy storage system (for nighttime power storage, cogeneration,photovoltaic power generation, or the like) or a energy storage systemof an electric vehicle and a secondary battery used for the system has alarge capacity and a high energy density. It is preferable for thesecondary battery to have an energy capacity of 30 Wh or more or it ismore preferable for the secondary battery to have an energy capacity of50 Wh or more. It is preferable for the secondary battery to have avolume energy density of 180 Wh/l or more or it is more preferable forthe secondary battery to have a volume energy density of 200 Wh/l. Whenthe energy capacity is less than 30 Wh or the volume energy density islower than 180 Wh/l, this method is not preferable because the capacityis too small to be used for a energy storage system it is necessary toincrease the numbers of batteries connected in series and in parallel inorder to obtain a sufficient system capacity, or a compact designbecomes difficult.

[0300] From the above viewpoints, a nickel-hydrogen battery or a lithiumsecondary battery provided with a non-aqueous electrolyte containinglithium salt is preferable as a secondary battery of the presentinvention and particularly, a lithium secondary battery is optimum.

[0301] It is preferable to use materials, dimensions, and shapes ofsecondary-battery components such as a positive electrode, negativeelectrode, separator, and the plate thickness of a battery case havingthe characteristics already described.

[0302] A secondary battery of the present invention is characterized bymeasuring the fluctuation of operation characteristics produced in abattery and controlling the battery in accordance with the measurementresult. Operation characteristics to be measured include not onlycharacteristics directly related to charge and discharge operations suchas voltage, current, temperature, and internal resistance but alsocharacteristics indirectly related to charge and discharge operationssuch as dimension and pressure to be changed due to gas generationcaused under severe operations. It is possible to use various measuringmeans normally used for these characteristics for measurement. Thoughthe number of measuring points in a battery (in a single cell) isdetermined in accordance with the shape of a battery, requested controlaccuracy, or measuring means, it is preferable to measure at least oneoperation characteristic at at least 2 points and compare measurementresults.

[0303] For example, when selecting a voltage as an operationcharacteristic to be measured, it is possible to know the fluctuation ofvoltages in a battery by measuring voltages at a plurality of points ofthe battery or measuring an electrode terminal voltage and a voltage atone point or voltages at a plurality of points of the battery andcomparing them. When m asuring t mperature as an operationcharacteristic, it is possible to know th fluctuation of temperatures ina battery by comparing the temperatures at a plurality of points such asthe inner portion and the vicinity of the surface of a battery, aterminal and the surface of a battery case, an upper portion a and lowerportion of a battery case, and so on. When measuring a dimensionalchange of a battery case, it is possible to easily know the state of abattery by measuring the thickness of the battery. In this case, it ispossible to know the fluctuation of dimensions of a battery,particularly the fluctuation of dimensional changes by measuring aplurality of battery thicknesses from the outside of the battery andcomparing the measured thicknesses.

[0304] It is possible to combine measurements of a plurality ofoperation characteristics. From the viewpoint of measurement efficiency,however, it is preferable to minimize the number of measuring points byselecting measuring points representing fluctuations of operationcharacteristics of a battery.

[0305] In the case of a control method of the present invention,fluctuation of operation characteristics of a secondary battery iscontrolled so as to eliminate or moderate the fluctuation or prevent thedeterioration of the safety and reliability. Control can be performed byvarious methods in accordance with the sort of operationcharacteristics. For example, when the fluctuation of differencesbetween surface temperature and internal temperature is m asured and itis determined that the fluctuation must be moderated, controls areperformed to lower the current of charge and discharge, to operate acooling of a fan, or to stop charge or discharge according to thecircumstances. When fluctuation of internal resistances betweenelectrodes in a battery occurs, there are some cases in which current isconcentrated on a portion having a small internal resistance and localovercharge occurs. In this case, by performing controls of pressing fromthe outside of a battery case and reduction of charge rate, it ispossible to prevent local overcharge and secure the safety depending onthe fluctuation in internal resistance.

[0306] The method of the present invention for controlling a secondarybattery for a energy storage system can be applied to each cell or thecells selected according to a necessity in a module formed by combininga plurality of single cells or in a battery system formed by combiningthe modules. In this case, as a control mode, it is possible to useconventioally proposed cell basis control or module basis controltogether with cell by cell control of the present invention. Further, itis possible to control a module or battery system by utilizing thefluctuation information regarding each of different cells. For example,when each of the cells shows similar operation-characteristic,simultaneous control can be performed for each of the modules or wholeof the battery system.

[0307] It is possible to perform the control according to a safetyrequirement related to the amount of charged or discharged energy, insuch a manner that in a usual state charge or discharge is controlledbased on an operation characteristic, e.g. the measurement of thevoltage of a position of a battery, and a control based on a temperaturemeasurement is added when the amount of charged or discharged energy hasincreased, and a control base on a dimension measurement is added whenthe amount has further increased.

[0308] In the case of a secondary-battery control method of the presentinvention, a battery is charged by charging equipment such as aphotovoltaic cells, a commercial power system, or an electric generator,etc., and is discharged for loads such as a motor, an electric lamp, ahousehold unit, etc. Therefore, it is possible to perform a control byutilizing the operational information of the unit or equipment, or tooperate the unit or equipment in accordance with the state of thebattery.

[0309] In the case of the above-described secondary-battery controlmethod of the present invention, it is possible to improve thereliability and safety by performing control corresponding to thefluctuation of operation characteristics in a battery. However, it ispreferable to design a battery so as to reduce the fluctuation ofoperation characteristics in the battery. Therefore, in the case of thepresent invention, a battery is formed into a flat shape and thethickness of the battery is preferably less than 12 mm, more preferablyless than 10 mm, and still more preferably less than 8 mm. When thethickness of a battery is 12 mm or more, it is difficult to radiate theheat in the battery to the outside or the temperature difference betweenthe inner portion and the surface of the battery increases, thefluctuation in the battery increases, and control becomes complicated.

[0310] A control m thod of the present invention is more specificallydescribed below based on an embodiment of the control method.

[0311] (Embodiment 8-1)

[0312] (1) Positive-electrode mixture slurry was obtained by mixing 100parts by weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL; productNo. M063), 10 parts by weight of acetylene black, and 5 parts by weightof polyvinylidene fluoride (PVdF) with 100 parts by weight ofN-methylpyrrolidone (NMP). A positive electrode was obtained by applyingthe slurry to both sides of aluminum foil having a thickness of 20 mmand drying and pressing the foil. FIG. 15 is an illustration of anelectrode. In the case of this embodiment, the coating area (W1×W2) ofan electrode 1101 was 133×198 mm² and slurry was applied to both sidesof 20-mm aluminum foil 1102 at a thickness of 120 mm. As a result, theelectrode thickness was 260 mm. One of the edge portions of the currentcollector extending along the arrow W2 and having a width of 1 cm wasnot coated with the electrode, and a tab 1103 (aluminum having athickness of 0.1 mm and a width of 6 mm) was welded thereto.

[0313] (2) Negative-electrode mixture slurry was obtained by mixing 100parts by weight of graphitized mesocarbon microbeads (MCMB: made byOSAKA GAS CHEMICAL Co., Ltd.; product No. 628) and 10 parts by weight ofPVdF with 90 parts by weight of NMP. A negative electrode was obtainedby applying the slurry to both sides of copper foil having a thicknessof 14 mm and drying and pressing the foil. Because the shape of thenegative electrode is the same as the above positive electrode, thenegative electrode is described by referring to FIG. 15. In the case ofthis embodiment, the coating area (W1×W2) of the electrode 1101 was135×200 mm² and the slurry was applied to both sides of the copper foil1102 at a thickness of 80 mm. As a result, the electrode thickness t is174 mm. One of the edge portions of the current collector extendingalong the arrow W2 and having a width of 1 cm is not coated with theelectrode, and a tab 1103 (nickel having a thickness of 0.1 mm and awidth of 6 mm) is welded thereto.

[0314] Slurry was applied to only one side by the same method and asingle-sided electrode having a thickness of 94 mm was formed by thesame method other than the side. The single-sided electrode is set tothe outermost of the electrode-stacked body in the following Item (3)(1101 n′ in FIG. 17).

[0315] (3) Two electrode-stacked bodies were formed by alternatelystacking nine positive electrodes 1101 p and ten negative electrodes(eight both-sided electrodes 1101 n and two single-sided electrodes 1101n′) obtained in the above Item (1) with a separator 1104 (made by TONENTAPIRUSU Co., Ltd.; made of porous polyethylene) held between theelectrode as shown in FIG. 17.

[0316] (4) The battery bottom case (122 in FIG. 16) was formed bydeep-drawing a thin plate made of SUS304 having a thickness of 0.5 mm. Abattery case upper case (121 in FIG. 16) was also formed of a thin platemade of SUS304 having a thickness of 0.5 mm.

[0317] Terminals 113 and 0.114 made of SUS304 (diameter of 6 mm) and asafety-vent hole 117 (diameter of 8 mm) were formed on the battery caseupper case, and the terminals 113 and 114 were insulated from thebattery case upper case 111 by a polypropylene packing.

[0318] (5) Each of the positive terminals 1103 p of twoelectrode-stacked bodies formed in the above Item (3) was welded to theterminal 113 and each of the negative electrodes 1103 n of the bodieswas welded to the terminal 114 and then, the electrode-stacked bodieswere stacked on the battery bottom case 122 and fixed by an insulatingtape. To measure temperatures of portions X and Y in FIG. 17, a filmthermocouple made by Phillips Corp. was attached to thenegative-electrode current collector of each portion and the lead wireof each thermocouple was connected to the positive electrodes 115 p and116 p and negative electrodes 115 n and 116 n. A spacer 1105 was presentbetween two stacked bodies in order to form a space for accommodatingthe Y-portion thermocouple. Under the above state, the entirecircumference of the portion A in FIG. 16 was laser-welded. Thereafter,a solution made by dissolving LiPF₆ at a concentration of 1 mol/l in asolvent obtained by mixing ethylene carbonate and diethyl carbonate at aweight ratio of 1:1 was poured through a safety-vent hole as anelectrolyte and hole was closed by using aluminum foil having athickness of 0.1 mm. It is possible to measure the temperature nearbythe surface in the battery in accordance with the potential differencebetween the positive and negative terminals 115 pand 115 n and thetemperature of the inner portion in the battery in accordance with thepotential difference between 116 p and 116 n and to measure thetemperature fluctuation in the battery by comparing the above potentialdifferences.

[0319] (6) The formed battery has dimensions of 165×230 mm² and athickness of 10 mm. The obtained battery was charged by aconstant-current/constant-voltage charging for 8 hours, in which thebattery was charged up to 4.3 V by a current of 10 A and then charged bya constant voltage of 4.3 V. Then, the battery was discharged up to 2.0V by a current of 30 A. The discharge capacity was 22 Ah, energycapacity was 78 Wh, and energy density was 205 Wh/l.

[0320] (7) The battery was charged and discharged under the conditionsin the above Item (6) while measuring temperatures of the X and Yportions. However, when a difference occurred between internaltemperature and external temperature, charge or discharge was stoppedand charge and discharge were repeated so that the fluctuation ofinternal and external temperatures did not occur. As a result, chargeand discharge could be performed up to 10 cycles.

COMPARATIVE EXAMPLE 8-1 For Comparison With Embodiment 8-1

[0321] Charge and discharge were repeated 10 times by using a batteryand charge and discharge conditions same as the case of the embodimentunder a constant condition without control according to measurement ofthe internal temperature of the battery. As a result, the thickness ofthe battery was increased and the internal resistance was raised.

[0322] (Embodiment 8-2)

[0323] (1) Positive-electrode mixture slurry was obtained by mixing 100parts by weight of spinel-type LiMn₂O₄ (made by SEIMI CHEMICAL; productNo. M063), 10 parts by weight of acetylene black, and 5 parts by weightof PVDF with 100 parts by weight of NMP. A positive electrode wasobtained by applying the slurry to both sides of aluminum foil having athickness of 20 mm and drying and pressing the foil. FIG. 18 is anillustration of an electrode. In the case of this embodiment, thecoating area (W1×W2) of an electrode 1201 was 258×168 mm² and slurry wasapplied to both sides of 20-mm aluminum foil 1202 at a thickness of 120mm. As a result, the electrode thickness t was 260 mm. Both of the edgeportions and the central portion of the current collector in the view ofthe longitudinal direction of the collector was not coated with theelectrode in the width of 1 cm, and a tabs 1203 a, 1203 b, and 1203 c(aluminum having a thickness of 0.1 mm and a width of 4 mm) was weldedthereto.

[0324] A measuring electrode having measuring electrodes 1204 a, 1204 b,and 1204 c was formed in order to measure the fluctuation of internalvoltages. The electrode was formed by welding a 3 mm-square expand metal(aluminum) having a thickness of 50 mm to one end of a slender piece ofstainless-steel foil having a width of 3 mm and a thickness of 10 mm,attaching the expand metal to the surface of a positive electrode in abattery, bonding the stainless-steel foil to the positive electrodewhile insulating it from the positive electrode, and positioning theother end of the piece of the foil to protrude beyond an edge of thepositive electrode to form a terminal.

[0325] (2) Negative-electrode mixture slurry was obtained by mixing 100parts by weight of graphitized mesocarbon microbeads (MCMB) and 10 partsby weight of PVDF with 90 parts by weight of NMP. A negative electrodewas obtained by applying the slurry to both sides of a copper foilhaving a thickness of 14 mm and drying and pressing the foil. Becausethe shape of the negative electrode is the same as the above positiveelectrode, the negative electrode is described by referring to FIG. 18.In the case of this embodiment, the coating area (W1×W2) of theelectrode 1201 is 260×170 mm² and the slurry was applied to both sidesof the copper foil 1202 of 14 mm at a thickness of 80 mm. As a result,the electrode thickness t was 174 mm. Both of the edge portions and thecentral portion of the current collector in the view of the longitudinaldirection of the collector was not coated with the electrode in thewidth of 1 cm, and a tabs 1203 a′, 1203 b′, and 1203 c′ (copper having athickness of 0.1 mm and a width of 4 mm) was welded thereto.

[0326] To measure the fluctuation of internal voltages, measuringelectrodes having protruded ends as measuring electrodes 1204 a′, 1204b′, and 1204 c′ were formed, in the same manner as in the positiveelectrode, by welding a 3 mm-square expand metal (copper) having athickness of 50 mm to an end of a slender piece of stainless-steel foilhaving a width of 3 mm and a thickness of 10 mm.

[0327] Furthermore, slurry was applied to only one side by the samemethod and a single-sided electrode having a thickness of 94 mm wasformed by the same method other than the single-sided application of theslurry. The single-sided electrode was set to the outermost of theelectrode-stacked body stated in the following Item (3) (1201 n′ in FIG.19).

[0328] (3) An electrode-stacked body was formed by alternately stackingten positive electrodes 1201 p and eleven negative electrodes (nineboth-sided electrodes 1201 n and two single-sided electrodes 1201 n′)obtained in the above Item (1) with a separator 1205 (made by TONENTAPIRUSU Co., Ltd.; made of porous polyethylene) held between each ofthe electrode as shown in FIG. 19. A separator made of polypropylenenon-woven fabric having a thickness of 100 mm was set between electrodesprovided with internal-potential measuring terminals. The positiveelectrodes and negative electrodes were stacked so that their terminalsprotrude in mutually opposite direction.

[0329] (4) A battery bottom case (same as symbol 122 in FIG. 16) wasformed by deep-drawing a thin plate made of SUS304 having a thickness of0.5 mm. The battery upper case (symbol 1211 in FIG. 20) was also formedof a thin plate made of SUS304 having a thickness of 0.5 mm. Thefollowing were formed on the battery upper case as shown in FIG. 20:charge-discharge terminals 1213 a, 1213 b and 1213 c, 1214 a, 1214 b and1214 c (diameter of 6 mm) which were made of SUS304, voltage-measuringterminals 1215 a, 1215 b and 1215 c, and 1216 a, 1216 b and 1216 c(diameter of 3 mm), and a safety-vent hole 117 (diameter of 8 mm). Theterminals 1213 a, 1213 b and 1213 c, and 1214 a, 1214 b and 1214 c, 1215a, 1215 b and 1215 c, and 1216 a, 1216 b and 1216 c were insulated fromthe battery upper case 1211 by a polypropylene packing.

[0330] (5) A series of charge-discharge positive and negative electrodesand their positive-electrode- and negative-electrode-voltage measuringterminals on two electrode stacked bodies formed in the above Item (3)were welded to connection terminals on the battery case throughconnection lines as shown below. Connection terminal on Terminal ofelectrode-layered body battery case Charge-discharge positive-electrodetab 1203a Terminal 1213a Charge-discharge positive-electrode tab 1203bTerminal 1213b Charge-discharge positive-electrode tab 1203c Terminal1213c Charge-discharge negative-electrode tab 1203a Terminal 1214aCharge-discharge negative-electrode tab 1203b′ Terminal 1214bCharge-discharge negative-electrode tab 1203c′ Terminal 1214cPositive-electrode measuring electrode 1204a Terminal 1215aPositive-electrode measuring electrode 1204b Terminal 1215bPositive-electrode measuring electrode 1204c Terminal 1215cNegative-electrode measuring electrode 1204a′ Terminal 1216aNegative-electrode measuring electrode 1204b′ Terminal 1216bNegative-electrode measuring electrode 1204c′ Terminal 1216c

[0331] Thereafter, the electrode-stacked bodies were stacked on thebottom of the battery bottom case 122 and fixed by an insulating tape,and the entire circumference of a portion corresponding to the edgyportion A in FIG. 16 was laser-welded. Thereafter, a solution was madeby dissolving LiPF₆ at a concentration of 1 mol/l in a solvent obtainedby mixing ethylene carbonate and diethyl carbonate at a weight ratio of.1:1. The solution was poured through a safety-vent hole 117 as anelectrolyte and the hole was closed by using aluminum foil having athickness of 0.1 mm.

[0332] (6) The formed battery has dimensions of 300×210 mm² and athickness of 6 mm. The battery was charged and discharged so that apotential difference did not occur between thepositive-electrode-voltage measuring terminals 1215 a, 1215 b, and 1215c or between the negative-electrode-voltage measuring terminals 1216 a,1216 b, and 1216 c by measuring the potential difference between thepositive-electrode-voltage measuring t rminals 1215 a, 1215 b, and 1215c and th potential difference between the negative-electrode-voltagemeasuring terminals 1216 a, 1216 b, and 1216 c and controlling thecurrent to be supplied to the charge-discharge terminals (positiveterminals 1213 a, 1213 b, and 1213 c and the negative terminals 1214 a,1214 b, and 1214 c). That is, charge and discharge were controlled so asto eliminate the fluctuation of potentials for charge and discharge incells. The battery was charged by a constant-current/constant-voltagecharging for 8 hours, in which the battery was charged up to 4.3 V(potential between terminals 1213 b and 1214 b) by a current of 10 A andthen charged by a constant voltage of 4.3 V.

[0333] Then, the battery was discharged up to 2.0 V by a constantcurrent of 5 A. The discharge capacity was 23 Ah, energy capacity was 81Wh, and volume energy density was 210 Wh/l.

[0334] (7) Charge and discharge were repeated 10 times while performingthe above control. For comparison, the same level of charge anddischarge were repeated 10 times only by the connection to the terminaland electrode 1213 a and 1214 a. As a result, the battery controlled inaccordance with the method of the embodiment was less deteriorated incapacity. Now, description of methods of the present invention iscompleted.

[0335] As described above, according to the present invention, it ispossible to provide a non-aqueous secondary battery applicable to energystorage which has a large capacity of 30 Wh or more and a volume energydensity of 180 Wh/l or more and is superior in heat radiationcharacteristic and safely used. By a specific negative lectrodeprovided, it is possible to provide a non-aqueous secondary batteryapplicable to energy storage system and having features of largecapacity and high safety.

[0336] Furthermore, according to the present invention, it is possibleto provide a flat non-aqueous secondary battery, particularly a flatbattery having a large capacity and a high volume energy density, whichis further superior in cycle characteristic by comprising one type ofseparator or two types or more of separators having a specificresiliency.

[0337] Furthermore, according to the present invention, it is possibleto provide a flat non-aqueous secondary battery, particularly a flatbattery having a large capacity and a high volume energy density, whichis superior in heat radiation characteristic, and has a low probabilityof making short circuit during assembling of a battery based on thebonding of a separator with an electrode.

[0338] Furthermore, according to a control method of the presentinvention, reliabilities such as safety and cycle characteristic of abattery are further improved because of measuring the fluctuation ofoperation characteristics in the battery and controlling charge anddischarge in accordance with the measurement results.

[0339] Furthermore, according to a secondary battery of the presentinvention provided with positive and negative terminals for charge anddischarge and terminals for measuring internal operationcharacteristics, it is possible to easily and securely perform the abovecontrol.

What is claimed is:
 1. A non-aqueous secondary battery comprisingpositive and negative electrodes and a lithium salt-containingelectrolyte, the battery being at least 30 Wh in energy capacity and atleast 180 Wh/l in volume energy density and having a flat shape with athickness of less than 12 mm.
 2. The non-aqueous secondary batteryaccording to claim 1, wherein the positive electrode contains manganeseoxide.
 3. The non-aqueous secondary battery according to claim 1 or 2,wherein the negative electrode is formed by using graphite having anaverage particle diameter of 1 to 50 mm as active material, a resin asbinder, and a metal as current collector, the negative electrode havinga porosity of 20 to 35%, an electrode density of 1.40 to 1.70 g/cm³, andan capacity of electrode of 400 Ah/cm³ or higher.
 4. The non-aqueoussecondary battery according to claim 3, wherein the negative electrodecontains a graphite material obtained by graphitizing mesocarbonmicrobeads.
 5. The non-aqueous secondary battery according to claim 1 or2, wherein the negative electrode comprises as active materialdouble-structure graphite particles formed with graphite-based particlesand amorphous carbon layers covering the surface of the graphite-basedparticles, the graphite-based particles having (d002) spacing of (002)planes of not more than 0.34 nm as measured by X-ray wide-anglediffraction method, the amorphous carbon layers having (d002) spacing of(002) planes of 0.34 nm or higher.
 6. The non-aqueous secondary batteryaccording to claim 5, wherein the negativ electrode is formed by usingdouble-structure graphite particles having an average particle diam terof 1 to 50 mm as active material, a resin as binder, and a metal ascurrent collector, the negative electorode having a porosity of 20 to35%, an electrode density of 1.20 to 1.60 g/cm³ , and an capacity ofelectrode of 400 mAh/cm³ or higher.
 7. The non-aqueous secondary batteryaccording to claim 1 or 2, wherein the negative electrode comprises asactive material a carbon material manufactured by mixing at least one ofartificial graphite and natural graphite with a carbon material havingvolatile components on the surface and/or in the inside and baking themixture.
 8. The non-aqueous secondary battery according to claim 7,wherein the negative electrode is formed by using a resin as binder anda metal as current collector, the negative electrode having a porosityof 20 to 35%, an electrode density of 1.20 to 1.60 g/cm³, and ancapacity of electrode of 400 mAh/cm³ or higher.
 9. The non-aqueoussecondary battery according to claim 1, wherein the front and rear sidesof the flat shape are rectangular.
 10. The non-aqueous secondary batteryaccording to claim 1, wherein the wall thickness of a battery case ofthe non-aqueous secondary battery is not less than 0.2 mm and not morethan 1 mm.
 11. A secondary battery comprising a positive electrode, anegative electrode, a separator, and a non-aqueous electrolytecontaining lithium salt and having a flat shape.
 12. The non-aqueoussecondary battery according to claim 11, wherein when a pr ssure of 2.5kg/cm² is applied to the direction of thickness of the separator, thethickness A of the separator is not less than 0.02 mm and not more than0.15 mm and the porosity of the separator is 40% or higher, and when theabsolute value of a change rate of the thickness (mm) of the separatorrelative to the pressure (kg/cm²) applied to the direction of thicknessof the separator is defined as B. (mm/(kg/cm²)), the pressure F whichrenders B/A=1 is not less than 0.05 kg/cm² and not more than 1 kg/cm².13. The non-aqueous secondary battery according to claim 11, wherein theseparator has a first separator and a second separator different fromthe first separator, when a pressure of 2.5 kg/cm² is applied to thedirection of thickness of the separator, the thickness A of the firstseparator is not less than 0.02 mm and not more than 0.15 mm and theporosity of the first separator is 40% or higher, and when the absolutevalue of a change rate of the thickness (mm) of the first separatorrelative to the pressure (kg/cm²) applied to the direction of thicknessof the first separator is defined as B (mm/(kg/cm²)), the pressure Fwhich renders B/A=1 is not less than 0.05 kg/cm² and not more than 1kg/cm², and the second separator is a micro-porous film having athickness of 0.05 mm or less, a pore diameter of 5 mm or less, and aporosity of 25% or more.
 14. The non-aqueous secondary battery accordingto claim 11, wherein the separator is bonded with the positive electrodeand/or the negative electrode.
 15. The non-aqueous secondary batteryaccording to claim 14, wherein the separator is bonded with the positiveelectrode and the negative electrode by fusing part of the separatorand, passages for the non-aqueous electrolyte are formed to penetratethe separator from the front side surface to the rear side surfacethereof.
 16. The non-aqueous secondary battery according to any one ofclaims 12 to 15, wherein the non-aqueous secondary battery has a flatshape with a thickness of less than 12 mm and is at least 30 Wh inenergy capacity and at least 180 Wh/l in volume energy density.
 17. Thenon-aqueous secondary battery according to any one of claims 12 to 16,wherein the front side and the rear side of the flat shape arerectangular.
 18. The non-aqueous secondary battery according to any oneof claims 12 to 16, wherein the wall thickness of a battery case of thenon-aqueous secondary battery is not less than 0.2 and not more than 1mm.
 19. The non-aqueous secondary battery according to any one of claims12 to 15, wherein the separator is made of a material comprising atleast one of polyethylene or polypropylene as a main component.
 20. Thenon-aqueous secondary battery according to claim 12, wherein theseparator is made of non-woven fabric.
 21. The non-aqueous secondarybatt ry according to claim 20, wherein the unit weight of the separatoris not less than 5 and g/m² and not more than 30 g/m².
 22. Thenon-aqueous secondary battery according to claim 13, wherein the firstseparator is made of non-woven fabric.
 23. The non-aqueous secondarybattery according to claim 22, wherein the unit weight of the firstseparator is not less than 5 and g/m² and not more than 30 g/m².
 24. Thenon-aqueous secondary battery according to claim 13, wherein the firstand second separators are joined together integrally.
 25. Thenon-aqueous secondary battery according to claim 13, wherein thematerial of the first separator is different from that of the secondseparator.
 26. The non-aqueous secondary battery according to claim 13,wherein at least one of the first and second separators containpolyethylene.
 27. A secondary-battery control method to be applied tothe secondary battery of claim 1 or 11, comprising the steps ofmeasuring operational parameters of at different portions of the batteryand controlling operations of the battery based on the results of themeasurement.
 28. The secondary-battery control method according to claim27, wherein the operational parameters to be measured include at leastone of the voltage, tension of current, temperature, dimensions, andinternal resistance of a secondary battery.
 29. Th secondary-batterycontrol method according to claim 27, wherein charge and dischargeconditions and resting conditions of the battery, battery temperaturesadjusted by heating or cooling, and pressure against the battery caseare controlled based on the results of the measurement.
 30. A secondarybattery for a energy storage system, comprising positive and negativeterminals for charge and discharge provided on the battery case andoperation-parameter measuring electrodes extending from differentportions of the battery to the outside of the battery case formeasurement of the operation parameters in the battery.